diff --git a/.github/workflows/bc.yml_ b/.github/workflows/bc.yml_
index 5970206c..d2a73479 100644
--- a/.github/workflows/bc.yml_
+++ b/.github/workflows/bc.yml_
@@ -20,4 +20,4 @@ jobs:
       os: >-
         ['ubuntu-latest']
       php: >-
-        ['8.1']
+        ['8.4']
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 5f082ce5..162552b2 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -35,7 +35,7 @@ jobs:
     strategy:
       matrix:
         php:
-          - 8.3
+          - 8.4
 
         oracle:
           - 18
@@ -46,6 +46,8 @@ jobs:
             oracle: 21
           - php: 8.2
             oracle: 21
+          - php: 8.3
+            oracle: 21
 
     services:
       oci:
diff --git a/.github/workflows/composer-require-checker.yml b/.github/workflows/composer-require-checker.yml
index d37dffd5..daf22788 100644
--- a/.github/workflows/composer-require-checker.yml
+++ b/.github/workflows/composer-require-checker.yml
@@ -36,6 +36,7 @@ jobs:
           - 8.1
           - 8.2
           - 8.3
+          - 8.4
 
     steps:
       - name: Checkout.
diff --git a/.github/workflows/mutation.yml b/.github/workflows/mutation.yml
index d2232faa..f57b2909 100644
--- a/.github/workflows/mutation.yml
+++ b/.github/workflows/mutation.yml
@@ -34,7 +34,7 @@ jobs:
           - ubuntu-latest
 
         php:
-          - 8.3
+          - 8.4
 
     services:
       oci:
diff --git a/.github/workflows/rector.yml b/.github/workflows/rector.yml
index 73c9d27f..4f252850 100644
--- a/.github/workflows/rector.yml
+++ b/.github/workflows/rector.yml
@@ -19,4 +19,4 @@ jobs:
       os: >-
         ['ubuntu-latest']
       php: >-
-        ['8.3']
+        ['8.4']
diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
index 2f4ca817..47eff664 100644
--- a/.github/workflows/static.yml
+++ b/.github/workflows/static.yml
@@ -35,9 +35,10 @@ jobs:
           - ubuntu-latest
 
         php:
-          - '8.1'
-          - '8.2'
-          - '8.3'
+          - 8.1
+          - 8.2
+          - 8.3
+          - 8.4
 
     steps:
       - name: Checkout.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index b100f4cb..cb825738 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,8 @@
 - New #301: Add `IndexType` class (@Tigrov)
 - New #303: Support JSON type (@Tigrov)
 - Bug #305: Explicitly mark nullable parameters (@vjik)
+- Chg #306: Change supported PHP versions to `8.1 - 8.4` (@Tigrov)
+- Enh #306: Minor refactoring (@Tigrov)
 - New #307: Add parameters `$ifExists` and `$cascade` to `CommandInterface::dropTable()` and
   `DDLQueryBuilderInterface::dropTable()` methods (@vjik)
 
diff --git a/README.md b/README.md
index 7fd86da3..188b0d33 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,7 @@ your Oracle database and perform various database operations as needed.
 
 | PHP           | Oracle Version | CI-Actions |
 |---------------|----------------|------------|
-| **8.1 - 8.3** | **12c - 21c**|[![build](https://github.com/yiisoft/db-oracle/actions/workflows/build.yml/badge.svg?branch=dev)](https://github.com/yiisoft/db-oracle/actions/workflows/build.yml) [![Mutation testing badge](https://img.shields.io/endpoint?style=flat&url=https%3A%2F%2Fbadge-api.stryker-mutator.io%2Fgithub.com%2Fyiisoft%2Fdb-oracle%2Fmaster)](https://dashboard.stryker-mutator.io/reports/github.com/yiisoft/db-oracle/master) [![static analysis](https://github.com/yiisoft/db-oracle/actions/workflows/static.yml/badge.svg?branch=dev)](https://github.com/yiisoft/db-oracle/actions/workflows/static.yml) [![type-coverage](https://shepherd.dev/github/yiisoft/db-oracle/coverage.svg)](https://shepherd.dev/github/yiisoft/db-oracle)
+| **8.1 - 8.4** | **12c - 21c**|[![build](https://github.com/yiisoft/db-oracle/actions/workflows/build.yml/badge.svg?branch=dev)](https://github.com/yiisoft/db-oracle/actions/workflows/build.yml) [![Mutation testing badge](https://img.shields.io/endpoint?style=flat&url=https%3A%2F%2Fbadge-api.stryker-mutator.io%2Fgithub.com%2Fyiisoft%2Fdb-oracle%2Fmaster)](https://dashboard.stryker-mutator.io/reports/github.com/yiisoft/db-oracle/master) [![static analysis](https://github.com/yiisoft/db-oracle/actions/workflows/static.yml/badge.svg?branch=dev)](https://github.com/yiisoft/db-oracle/actions/workflows/static.yml) [![type-coverage](https://shepherd.dev/github/yiisoft/db-oracle/coverage.svg)](https://shepherd.dev/github/yiisoft/db-oracle)
 
 ## Installation
 
diff --git a/composer.json b/composer.json
index 0ebf770a..0d1a01bf 100644
--- a/composer.json
+++ b/composer.json
@@ -31,20 +31,20 @@
     ],
     "require": {
         "ext-pdo": "*",
-        "php": "^8.1",
+        "php": "8.1 - 8.4",
         "yiisoft/db": "dev-master"
     },
     "require-dev": {
-        "maglnet/composer-require-checker": "^4.2",
-        "phpunit/phpunit": "^10.0",
-        "rector/rector": "^2.0",
-        "roave/infection-static-analysis-plugin": "^1.16",
-        "spatie/phpunit-watcher": "^1.23",
-        "vimeo/psalm": "^5.25",
-        "vlucas/phpdotenv": "^5.6",
+        "maglnet/composer-require-checker": "^4.7.1",
+        "phpunit/phpunit": "^10.5.45",
+        "rector/rector": "^2.0.10",
+        "roave/infection-static-analysis-plugin": "^1.35",
+        "spatie/phpunit-watcher": "^1.24",
+        "vimeo/psalm": "^5.26.1 || ^6.8.8",
+        "vlucas/phpdotenv": "^5.6.1",
         "yiisoft/aliases": "^2.0",
-        "yiisoft/cache-file": "^3.1",
-        "yiisoft/var-dumper": "^1.5"
+        "yiisoft/cache-file": "^3.2",
+        "yiisoft/var-dumper": "^1.7"
     },
     "autoload": {
         "psr-4": {
diff --git a/psalm.xml b/psalm.xml
index fc577119..6461f99d 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -1,9 +1,11 @@
 <?xml version="1.0"?>
 <psalm
   errorLevel="1"
+  ensureOverrideAttribute="false"
   findUnusedBaselineEntry="true"
   findUnusedCode="false"
   resolveFromConfigFile="true"
+  strictBinaryOperands="false"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns="https://getpsalm.org/schema/config"
   xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
diff --git a/src/Column/ColumnDefinitionParser.php b/src/Column/ColumnDefinitionParser.php
index e1f0055f..6aefed1c 100644
--- a/src/Column/ColumnDefinitionParser.php
+++ b/src/Column/ColumnDefinitionParser.php
@@ -29,7 +29,9 @@ public function parse(string $definition): array
     {
         preg_match(self::TYPE_PATTERN, $definition, $matches);
 
-        $type = strtolower(preg_replace('/\s*\(\d+\)/', '', $matches[4] ?? $matches[1]));
+        /** @var string $type */
+        $type = preg_replace('/\s*\(\d+\)/', '', $matches[4] ?? $matches[1]);
+        $type = strtolower($type);
         $info = ['type' => $type];
 
         $typeDetails = $matches[6] ?? $matches[2] ?? '';
diff --git a/src/Column/JsonColumn.php b/src/Column/JsonColumn.php
index e7797775..b6387a9e 100644
--- a/src/Column/JsonColumn.php
+++ b/src/Column/JsonColumn.php
@@ -28,7 +28,9 @@ public function phpTypecast(mixed $value): mixed
         }
 
         if (is_resource($value)) {
-            return json_decode(stream_get_contents($value), true, 512, JSON_THROW_ON_ERROR);
+            /** @var string */
+            $value = stream_get_contents($value);
+            return json_decode($value, true, 512, JSON_THROW_ON_ERROR);
         }
 
         return $value;
diff --git a/src/Command.php b/src/Command.php
index 196a6892..8fd58a4e 100644
--- a/src/Command.php
+++ b/src/Command.php
@@ -21,7 +21,7 @@
  */
 final class Command extends AbstractPdoCommand
 {
-    public function insertWithReturningPks(string $table, array $columns): bool|array
+    public function insertWithReturningPks(string $table, array $columns): array|false
     {
         $tableSchema = $this->db->getSchema()->getTableSchema($table);
         $returnColumns = $tableSchema?->getPrimaryKey() ?? [];
diff --git a/src/Schema.php b/src/Schema.php
index 0fa001c1..3b3f9454 100644
--- a/src/Schema.php
+++ b/src/Schema.php
@@ -446,7 +446,9 @@ protected function getTableSequenceName(string $tableName): string|null
      */
     private function loadColumn(array $info): ColumnInterface
     {
-        $dbType = strtolower(preg_replace('/\([^)]+\)/', '', $info['data_type']));
+        /** @var string $dbType */
+        $dbType = preg_replace('/\([^)]+\)/', '', $info['data_type']);
+        $dbType = strtolower($dbType);
 
         match ($dbType) {
             'timestamp',
diff --git a/tests/CommandTest.php b/tests/CommandTest.php
index 1ec58cb1..1c0bfba1 100644
--- a/tests/CommandTest.php
+++ b/tests/CommandTest.php
@@ -228,12 +228,12 @@ public function testCreateView(): void
         )->execute();
         $command->setSql(
             <<<SQL
-            INSERT INTO [[testCreateViewTable]] ("id", "bar") VALUES(testCreateTable_SEQ.NEXTVAL, 1)
+            INSERT INTO [[testCreateViewTable]] ("id", "bar") VALUES(testCreateViewTable_SEQ.NEXTVAL, 1)
             SQL,
         )->execute();
         $command->setSql(
             <<<SQL
-            INSERT INTO [[testCreateViewTable]] ("id", "bar") VALUES(testCreateTable_SEQ.NEXTVAL, 6)
+            INSERT INTO [[testCreateViewTable]] ("id", "bar") VALUES(testCreateViewTable_SEQ.NEXTVAL, 6)
             SQL,
         )->execute();
         $command->createView('{{testCreateView}}', $subquery)->execute();
@@ -640,12 +640,12 @@ public function testQueryScalarWithBlob(): void
         $this->assertEquals($value, $scalarValue);
     }
 
-    public function testProfiler(string $sql = null): void
+    public function testProfiler(string|null $sql = null): void
     {
         parent::testProfiler('SELECT 123 FROM DUAL');
     }
 
-    public function testProfilerData(string $sql = null): void
+    public function testProfilerData(string|null $sql = null): void
     {
         parent::testProfilerData('SELECT 123 FROM DUAL');
     }
diff --git a/tests/QuoterTest.php b/tests/QuoterTest.php
index 8f949d8c..5f665e68 100644
--- a/tests/QuoterTest.php
+++ b/tests/QuoterTest.php
@@ -38,7 +38,7 @@ public function testQuoteColumnName(string $columnName, string $expected): void
     public function testQuoteSimpleColumnName(
         string $columnName,
         string $expectedQuotedColumnName,
-        string $expectedUnQuotedColumnName = null
+        string|null $expectedUnQuotedColumnName = null
     ): void {
         parent::testQuoteSimpleColumnName($columnName, $expectedQuotedColumnName, $expectedUnQuotedColumnName);
     }