diff --git a/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpCount.php b/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpCount.php
new file mode 100644
index 00000000..0d601e49
--- /dev/null
+++ b/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpCount.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MartinGeorgiev\Doctrine\ORM\Query\AST\Functions;
+
+/**
+ * Implementation of PostgreSQL REGEXP_COUNT().
+ *
+ * Returns the number of times the POSIX regular expression pattern matches in the string.
+ *
+ * @see https://www.postgresql.org/docs/15/functions-matching.html#FUNCTIONS-POSIX-REGEXP
+ * @since 3.1
+ *
+ * @author Martin Georgiev <martin.georgiev@gmail.com>
+ *
+ * @example Using it in DQL: "SELECT REGEXP_COUNT(e.text, '\d\d\d', 1, 'i') FROM Entity e"
+ */
+class RegexpCount extends BaseVariadicFunction
+{
+    protected function getNodeMappingPattern(): array
+    {
+        return [
+            'StringPrimary,StringPrimary,ArithmeticPrimary,StringPrimary',
+            'StringPrimary,StringPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary',
+        ];
+    }
+
+    protected function getFunctionName(): string
+    {
+        return 'regexp_count';
+    }
+
+    protected function getMinArgumentCount(): int
+    {
+        return 2;
+    }
+
+    protected function getMaxArgumentCount(): int
+    {
+        return 4;
+    }
+}
diff --git a/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpInstr.php b/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpInstr.php
new file mode 100644
index 00000000..18989a82
--- /dev/null
+++ b/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpInstr.php
@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MartinGeorgiev\Doctrine\ORM\Query\AST\Functions;
+
+/**
+ * Implementation of PostgreSQL REGEXP_INSTR().
+ *
+ * Returns the position within string where the Nth match of the POSIX regular expression pattern occurs,
+ * or zero if there is no such match.
+ *
+ * @see https://www.postgresql.org/docs/17/functions-matching.html#FUNCTIONS-POSIX-REGEXP
+ * @since 3.1
+ *
+ * @author Martin Georgiev <martin.georgiev@gmail.com>
+ *
+ * @example Using it in DQL: "SELECT REGEXP_INSTR(e.text, 'c(.)(..)', 1, 1, 0, 'i', 2) FROM Entity e"
+ */
+class RegexpInstr extends BaseVariadicFunction
+{
+    protected function getNodeMappingPattern(): array
+    {
+        return [
+            'StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary,ArithmeticPrimary,StringPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary,ArithmeticPrimary,StringPrimary',
+            'StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary',
+        ];
+    }
+
+    protected function getFunctionName(): string
+    {
+        return 'regexp_instr';
+    }
+
+    protected function getMinArgumentCount(): int
+    {
+        return 2;
+    }
+
+    protected function getMaxArgumentCount(): int
+    {
+        return 7;
+    }
+}
diff --git a/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpReplace.php b/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpReplace.php
index 5276fb6a..2a426fb2 100644
--- a/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpReplace.php
+++ b/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpReplace.php
@@ -7,20 +7,41 @@
 /**
  * Implementation of PostgreSQL REGEXP_REPLACE().
  *
- * @see https://www.postgresql.org/docs/15/functions-matching.html#FUNCTIONS-POSIX-REGEXP
+ * Replaces substring(s) matching a POSIX regular expression pattern with a replacement string.
+ *
+ * @see https://www.postgresql.org/docs/17/functions-matching.html#FUNCTIONS-POSIX-REGEXP
  * @since 2.5
  *
  * @author Colin Doig
+ *
+ * @example Using it in DQL: "SELECT REGEXP_REPLACE(e.text, 'pattern', 'replacement', 3, 2, 'i') FROM Entity e"
  */
-class RegexpReplace extends BaseRegexpFunction
+class RegexpReplace extends BaseVariadicFunction
 {
+    protected function getNodeMappingPattern(): array
+    {
+        return [
+            'StringPrimary,StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary,StringPrimary',
+            'StringPrimary,StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary,StringPrimary,ArithmeticPrimary,StringPrimary',
+            'StringPrimary,StringPrimary,StringPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary,StringPrimary,StringPrimary',
+            'StringPrimary,StringPrimary,StringPrimary',
+        ];
+    }
+
     protected function getFunctionName(): string
     {
         return 'regexp_replace';
     }
 
-    protected function getParameterCount(): int
+    protected function getMinArgumentCount(): int
     {
         return 3;
     }
+
+    protected function getMaxArgumentCount(): int
+    {
+        return 6;
+    }
 }
diff --git a/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpSubstr.php b/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpSubstr.php
new file mode 100644
index 00000000..72441d80
--- /dev/null
+++ b/src/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpSubstr.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MartinGeorgiev\Doctrine\ORM\Query\AST\Functions;
+
+/**
+ * Implementation of PostgreSQL REGEXP_SUBSTR().
+ *
+ * Returns the substring within string that matches the Nth occurrence of the POSIX regular expression pattern,
+ * or NULL if there is no such match.
+ *
+ * @see https://www.postgresql.org/docs/15/functions-matching.html#FUNCTIONS-POSIX-REGEXP
+ * @since 3.1
+ *
+ * @author Martin Georgiev <martin.georgiev@gmail.com>
+ *
+ * @example Using it in DQL: "SELECT REGEXP_SUBSTR(e.text, 'c(.)(..)', 1, 1, 'i', 2) FROM Entity e"
+ */
+class RegexpSubstr extends BaseVariadicFunction
+{
+    protected function getNodeMappingPattern(): array
+    {
+        return [
+            'StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary,StringPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary,StringPrimary',
+            'StringPrimary,StringPrimary,ArithmeticPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary,ArithmeticPrimary',
+            'StringPrimary,StringPrimary',
+        ];
+    }
+
+    protected function getFunctionName(): string
+    {
+        return 'regexp_substr';
+    }
+
+    protected function getMinArgumentCount(): int
+    {
+        return 2;
+    }
+
+    protected function getMaxArgumentCount(): int
+    {
+        return 6;
+    }
+}
diff --git a/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpCountTest.php b/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpCountTest.php
new file mode 100644
index 00000000..88b871b2
--- /dev/null
+++ b/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpCountTest.php
@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\MartinGeorgiev\Doctrine\ORM\Query\AST\Functions;
+
+use Fixtures\MartinGeorgiev\Doctrine\Entity\ContainsTexts;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\BaseVariadicFunction;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\Exception\InvalidArgumentForVariadicFunctionException;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\RegexpCount;
+
+class RegexpCountTest extends BaseVariadicFunctionTestCase
+{
+    protected function createFixture(): BaseVariadicFunction
+    {
+        return new RegexpCount('REGEXP_COUNT');
+    }
+
+    protected function getStringFunctions(): array
+    {
+        return [
+            'REGEXP_COUNT' => RegexpCount::class,
+        ];
+    }
+
+    protected function getExpectedSqlStatements(): array
+    {
+        return [
+            'counts digits' => "SELECT regexp_count(c0_.text1, '\\d\\d\\d') AS sclr_0 FROM ContainsTexts c0_",
+            'counts words' => "SELECT regexp_count(c0_.text1, '\\w+') AS sclr_0 FROM ContainsTexts c0_",
+            'with start position' => "SELECT regexp_count(c0_.text1, '\\d\\d\\d', 1) AS sclr_0 FROM ContainsTexts c0_",
+            'with flags' => "SELECT regexp_count(c0_.text1, '\\d\\d\\d', 1, 'i') AS sclr_0 FROM ContainsTexts c0_",
+        ];
+    }
+
+    protected function getDqlStatements(): array
+    {
+        return [
+            'counts digits' => \sprintf("SELECT REGEXP_COUNT(e.text1, '\\d\\d\\d') FROM %s e", ContainsTexts::class),
+            'counts words' => \sprintf("SELECT REGEXP_COUNT(e.text1, '\\w+') FROM %s e", ContainsTexts::class),
+            'with start position' => \sprintf("SELECT REGEXP_COUNT(e.text1, '\\d\\d\\d', 1) FROM %s e", ContainsTexts::class),
+            'with flags' => \sprintf("SELECT REGEXP_COUNT(e.text1, '\\d\\d\\d', 1, 'i') FROM %s e", ContainsTexts::class),
+        ];
+    }
+
+    public function test_too_few_arguments_throws_exception(): void
+    {
+        $this->expectException(InvalidArgumentForVariadicFunctionException::class);
+        $this->expectExceptionMessage('regexp_count() requires at least 2 arguments');
+
+        $dql = \sprintf('SELECT REGEXP_COUNT(e.text1) FROM %s e', ContainsTexts::class);
+        $this->buildEntityManager()->createQuery($dql)->getSQL();
+    }
+
+    public function test_too_many_arguments_throws_exception(): void
+    {
+        $this->expectException(InvalidArgumentForVariadicFunctionException::class);
+        $this->expectExceptionMessage('regexp_count() requires between 2 and 4 arguments');
+
+        $dql = \sprintf("SELECT REGEXP_COUNT(e.text1, '\\d+', 1, 'i', 'extra_arg') FROM %s e", ContainsTexts::class);
+        $this->buildEntityManager()->createQuery($dql)->getSQL();
+    }
+}
diff --git a/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpInstrTest.php b/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpInstrTest.php
new file mode 100644
index 00000000..9961699b
--- /dev/null
+++ b/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpInstrTest.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\MartinGeorgiev\Doctrine\ORM\Query\AST\Functions;
+
+use Fixtures\MartinGeorgiev\Doctrine\Entity\ContainsTexts;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\BaseVariadicFunction;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\Exception\InvalidArgumentForVariadicFunctionException;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\RegexpInstr;
+
+class RegexpInstrTest extends BaseVariadicFunctionTestCase
+{
+    protected function createFixture(): BaseVariadicFunction
+    {
+        return new RegexpInstr('REGEXP_INSTR');
+    }
+
+    protected function getStringFunctions(): array
+    {
+        return [
+            'REGEXP_INSTR' => RegexpInstr::class,
+        ];
+    }
+
+    protected function getExpectedSqlStatements(): array
+    {
+        return [
+            'finds position of pattern' => "SELECT regexp_instr(c0_.text1, 'c(.)(...)') AS sclr_0 FROM ContainsTexts c0_",
+            'finds position of digits' => "SELECT regexp_instr(c0_.text1, '\\d+') AS sclr_0 FROM ContainsTexts c0_",
+            'with start position' => "SELECT regexp_instr(c0_.text1, '\\d+', 1) AS sclr_0 FROM ContainsTexts c0_",
+            'with start and occurrence' => "SELECT regexp_instr(c0_.text1, '\\d+', 1, 2) AS sclr_0 FROM ContainsTexts c0_",
+            'with start, occurrence and return_option' => "SELECT regexp_instr(c0_.text1, '\\d+', 1, 2, 0) AS sclr_0 FROM ContainsTexts c0_",
+            'with flags' => "SELECT regexp_instr(c0_.text1, '\\d+', 1, 2, 0, 'i') AS sclr_0 FROM ContainsTexts c0_",
+            'with subexpr' => "SELECT regexp_instr(c0_.text1, '\\d+', 1, 2, 0, 'i', 2) AS sclr_0 FROM ContainsTexts c0_",
+        ];
+    }
+
+    protected function getDqlStatements(): array
+    {
+        return [
+            'finds position of pattern' => \sprintf("SELECT REGEXP_INSTR(e.text1, 'c(.)(...)') FROM %s e", ContainsTexts::class),
+            'finds position of digits' => \sprintf("SELECT REGEXP_INSTR(e.text1, '\\d+') FROM %s e", ContainsTexts::class),
+            'with start position' => \sprintf("SELECT REGEXP_INSTR(e.text1, '\\d+', 1) FROM %s e", ContainsTexts::class),
+            'with start and occurrence' => \sprintf("SELECT REGEXP_INSTR(e.text1, '\\d+', 1, 2) FROM %s e", ContainsTexts::class),
+            'with start, occurrence and return_option' => \sprintf("SELECT REGEXP_INSTR(e.text1, '\\d+', 1, 2, 0) FROM %s e", ContainsTexts::class),
+            'with flags' => \sprintf("SELECT REGEXP_INSTR(e.text1, '\\d+', 1, 2, 0, 'i') FROM %s e", ContainsTexts::class),
+            'with subexpr' => \sprintf("SELECT REGEXP_INSTR(e.text1, '\\d+', 1, 2, 0, 'i', 2) FROM %s e", ContainsTexts::class),
+        ];
+    }
+
+    public function test_too_few_arguments_throws_exception(): void
+    {
+        $this->expectException(InvalidArgumentForVariadicFunctionException::class);
+        $this->expectExceptionMessage('regexp_instr() requires at least 2 arguments');
+
+        $dql = \sprintf('SELECT REGEXP_INSTR(e.text1) FROM %s e', ContainsTexts::class);
+        $this->buildEntityManager()->createQuery($dql)->getSQL();
+    }
+
+    public function test_too_many_arguments_throws_exception(): void
+    {
+        $this->expectException(InvalidArgumentForVariadicFunctionException::class);
+        $this->expectExceptionMessage('regexp_instr() requires between 2 and 7 arguments');
+
+        $dql = \sprintf("SELECT REGEXP_INSTR(e.text1, 'c(.)(..)', 1, 1, 0, 'i', 2, 'extra_arg') FROM %s e", ContainsTexts::class);
+        $this->buildEntityManager()->createQuery($dql)->getSQL();
+    }
+}
diff --git a/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpReplaceTest.php b/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpReplaceTest.php
index 4e8d46a5..17ea390d 100644
--- a/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpReplaceTest.php
+++ b/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpReplaceTest.php
@@ -5,10 +5,17 @@
 namespace Tests\MartinGeorgiev\Doctrine\ORM\Query\AST\Functions;
 
 use Fixtures\MartinGeorgiev\Doctrine\Entity\ContainsTexts;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\BaseVariadicFunction;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\Exception\InvalidArgumentForVariadicFunctionException;
 use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\RegexpReplace;
 
-class RegexpReplaceTest extends TestCase
+class RegexpReplaceTest extends BaseVariadicFunctionTestCase
 {
+    protected function createFixture(): BaseVariadicFunction
+    {
+        return new RegexpReplace('REGEXP_REPLACE');
+    }
+
     protected function getStringFunctions(): array
     {
         return [
@@ -19,14 +26,42 @@ protected function getStringFunctions(): array
     protected function getExpectedSqlStatements(): array
     {
         return [
-            "SELECT regexp_replace(c0_.text1, 'pattern', 'replacement') AS sclr_0 FROM ContainsTexts c0_",
+            'basic replacement' => "SELECT regexp_replace(c0_.text1, 'pattern', 'replacement') AS sclr_0 FROM ContainsTexts c0_",
+            'with flags but no start position' => "SELECT regexp_replace(c0_.text1, 'pattern', 'replacement', 'i') AS sclr_0 FROM ContainsTexts c0_",
+            'with start position' => "SELECT regexp_replace(c0_.text1, 'pattern', 'replacement', 3) AS sclr_0 FROM ContainsTexts c0_",
+            'with start position and flags' => "SELECT regexp_replace(c0_.text1, 'pattern', 'replacement', 3, 'i') AS sclr_0 FROM ContainsTexts c0_",
+            'with occurrence count but no flags' => "SELECT regexp_replace(c0_.text1, 'pattern', 'replacement', 3, 2) AS sclr_0 FROM ContainsTexts c0_",
+            'with occurrence count and flags' => "SELECT regexp_replace(c0_.text1, 'pattern', 'replacement', 3, 2, 'i') AS sclr_0 FROM ContainsTexts c0_",
         ];
     }
 
     protected function getDqlStatements(): array
     {
         return [
-            \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern', 'replacement') FROM %s e", ContainsTexts::class),
+            'basic replacement' => \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern', 'replacement') FROM %s e", ContainsTexts::class),
+            'with flags but no start position' => \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern', 'replacement', 'i') FROM %s e", ContainsTexts::class),
+            'with start position' => \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern', 'replacement', 3) FROM %s e", ContainsTexts::class),
+            'with start position and flags' => \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern', 'replacement', 3, 'i') FROM %s e", ContainsTexts::class),
+            'with occurrence count but no flags' => \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern', 'replacement', 3, 2) FROM %s e", ContainsTexts::class),
+            'with occurrence count and flags' => \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern', 'replacement', 3, 2, 'i') FROM %s e", ContainsTexts::class),
         ];
     }
+
+    public function test_too_few_arguments_throws_exception(): void
+    {
+        $this->expectException(InvalidArgumentForVariadicFunctionException::class);
+        $this->expectExceptionMessage('regexp_replace() requires at least 3 arguments');
+
+        $dql = \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern') FROM %s e", ContainsTexts::class);
+        $this->buildEntityManager()->createQuery($dql)->getSQL();
+    }
+
+    public function test_too_many_arguments_throws_exception(): void
+    {
+        $this->expectException(InvalidArgumentForVariadicFunctionException::class);
+        $this->expectExceptionMessage('regexp_replace() requires between 3 and 6 arguments');
+
+        $dql = \sprintf("SELECT REGEXP_REPLACE(e.text1, 'pattern', 'replacement', 3, 2, 'i', 'extra_arg') FROM %s e", ContainsTexts::class);
+        $this->buildEntityManager()->createQuery($dql)->getSQL();
+    }
 }
diff --git a/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpSubstrTest.php b/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpSubstrTest.php
new file mode 100644
index 00000000..8abb2f28
--- /dev/null
+++ b/tests/MartinGeorgiev/Doctrine/ORM/Query/AST/Functions/RegexpSubstrTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\MartinGeorgiev\Doctrine\ORM\Query\AST\Functions;
+
+use Fixtures\MartinGeorgiev\Doctrine\Entity\ContainsTexts;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\BaseVariadicFunction;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\Exception\InvalidArgumentForVariadicFunctionException;
+use MartinGeorgiev\Doctrine\ORM\Query\AST\Functions\RegexpSubstr;
+
+class RegexpSubstrTest extends BaseVariadicFunctionTestCase
+{
+    protected function createFixture(): BaseVariadicFunction
+    {
+        return new RegexpSubstr('REGEXP_SUBSTR');
+    }
+
+    protected function getStringFunctions(): array
+    {
+        return [
+            'REGEXP_SUBSTR' => RegexpSubstr::class,
+        ];
+    }
+
+    protected function getExpectedSqlStatements(): array
+    {
+        return [
+            'extracts pattern' => "SELECT regexp_substr(c0_.text1, 'c(.)(...)') AS sclr_0 FROM ContainsTexts c0_",
+            'extracts digits' => "SELECT regexp_substr(c0_.text1, '\\d+') AS sclr_0 FROM ContainsTexts c0_",
+            'extracts digits with start and N parameters' => "SELECT regexp_substr(c0_.text1, '\\d+', 1, 4) AS sclr_0 FROM ContainsTexts c0_",
+            'extracts digits with start and N parameters and flags' => "SELECT regexp_substr(c0_.text1, '\\d+', 1, 4, 'i') AS sclr_0 FROM ContainsTexts c0_",
+            'extracts digits with start, N parameters, flags and subexpr parameter' => "SELECT regexp_substr(c0_.text1, '\\d+', 1, 4, 'i', 3) AS sclr_0 FROM ContainsTexts c0_",
+        ];
+    }
+
+    protected function getDqlStatements(): array
+    {
+        return [
+            'extracts pattern' => \sprintf("SELECT REGEXP_SUBSTR(e.text1, 'c(.)(...)') FROM %s e", ContainsTexts::class),
+            'extracts digits' => \sprintf("SELECT REGEXP_SUBSTR(e.text1, '\\d+') FROM %s e", ContainsTexts::class),
+            'extracts digits with start and N parameters' => \sprintf("SELECT REGEXP_SUBSTR(e.text1, '\\d+', 1, 4) FROM %s e", ContainsTexts::class),
+            'extracts digits with start and N parameters and flags' => \sprintf("SELECT REGEXP_SUBSTR(e.text1, '\\d+', 1, 4, 'i') FROM %s e", ContainsTexts::class),
+            'extracts digits with start, N parameters, flags and subexpr parameter' => \sprintf("SELECT REGEXP_SUBSTR(e.text1, '\\d+', 1, 4, 'i', 3) FROM %s e", ContainsTexts::class),
+        ];
+    }
+
+    public function test_too_few_arguments_throws_exception(): void
+    {
+        $this->expectException(InvalidArgumentForVariadicFunctionException::class);
+        $this->expectExceptionMessage('regexp_substr() requires at least 2 arguments');
+
+        $dql = \sprintf('SELECT REGEXP_SUBSTR(e.text1) FROM %s e', ContainsTexts::class);
+        $this->buildEntityManager()->createQuery($dql)->getSQL();
+    }
+
+    public function test_too_many_arguments_throws_exception(): void
+    {
+        $this->expectException(InvalidArgumentForVariadicFunctionException::class);
+        $this->expectExceptionMessage('regexp_substr() requires between 2 and 6 arguments');
+
+        $dql = \sprintf("SELECT REGEXP_SUBSTR(e.text1, 'c(.)(..)', 1, 1, 'i', 1, 'extra_arg') FROM %s e", ContainsTexts::class);
+        $this->buildEntityManager()->createQuery($dql)->getSQL();
+    }
+}