feat(builder): add ColumnType for type-safe column definitions in CreateBuilder

- Add ColumnType final class with 25 fixed-type constants (TINYINT through
  UUID), 7 parameterised factory methods (varChar, charType, decimal,
  numeric, binary, varBinary, timestamp), and 4 chainable modifier methods
  (notNull, unique, autoIncrement, defaultValue)
- Add CreateBuilder.column(String, ColumnType) overload; delegates to the
  existing column(String, String) via ColumnType.toSql() — fully backward
  compatible
- Add ColumnTypeTest: 32 tests covering constants, factories, modifiers,
  chaining, and CreateBuilder integration

Author: ez-plugins

src/main/java/com/github/ezframework/javaquerybuilder/query/builder/ColumnType.java

@@ -0,0 +1,297 @@
+package com.github.ezframework.javaquerybuilder.query.builder;
+
+/**
+ * Type-safe column type definitions for use with
+ * {@link CreateBuilder#column(String, ColumnType)}.
+ *
+ * <p>Use the pre-defined constants for fixed-width types, the static factory
+ * methods for parameterised types, and the modifier methods to append
+ * column-level constraints:</p>
+ *
+ * <pre>{@code
+ * QueryBuilder.createTable("users")
+ *     .column("id",         ColumnType.INT.notNull().autoIncrement())
+ *     .column("username",   ColumnType.varChar(64).notNull().unique())
+ *     .column("balance",    ColumnType.decimal(10, 2))
+ *     .column("created_at", ColumnType.TIMESTAMP)
+ *     .primaryKey("id")
+ *     .build();
+ * // → CREATE TABLE users (
+ * //       id         INT NOT NULL AUTO_INCREMENT,
+ * //       username   VARCHAR(64) NOT NULL UNIQUE,
+ * //       balance    DECIMAL(10, 2),
+ * //       created_at TIMESTAMP,
+ * //       PRIMARY KEY (id))
+ * }</pre>
+ *
+ * <p>Raw SQL type strings are still accepted by
+ * {@link CreateBuilder#column(String, String)} for any type not covered here.</p>
+ *
+ * @author EzFramework
+ * @version 1.1.0
+ */
+public final class ColumnType {
+
+    // ── Exact-width integer types ──────────────────────────────────────────
+
+    /** 1-byte signed integer ({@code TINYINT}). Supported by MySQL, MariaDB. */
+    public static final ColumnType TINYINT = new ColumnType("TINYINT");
+
+    /** 2-byte signed integer ({@code SMALLINT}). */
+    public static final ColumnType SMALLINT = new ColumnType("SMALLINT");
+
+    /** 4-byte signed integer ({@code INT}). */
+    public static final ColumnType INT = new ColumnType("INT");
+
+    /** 4-byte signed integer ({@code INTEGER}). Alias for {@link #INT} in most databases. */
+    public static final ColumnType INTEGER = new ColumnType("INTEGER");
+
+    /** 8-byte signed integer ({@code BIGINT}). */
+    public static final ColumnType BIGINT = new ColumnType("BIGINT");
+
+    // ── Floating-point types ───────────────────────────────────────────────
+
+    /** Single-precision floating point ({@code FLOAT}). */
+    public static final ColumnType FLOAT = new ColumnType("FLOAT");
+
+    /** Double-precision floating point ({@code DOUBLE}). */
+    public static final ColumnType DOUBLE = new ColumnType("DOUBLE");
+
+    /** Double-precision floating point ({@code REAL}). Standard SQL alias for {@link #DOUBLE}. */
+    public static final ColumnType REAL = new ColumnType("REAL");
+
+    // ── Boolean ───────────────────────────────────────────────────────────
+
+    /** Boolean value ({@code BOOLEAN}). */
+    public static final ColumnType BOOLEAN = new ColumnType("BOOLEAN");
+
+    // ── Fixed-size text types ──────────────────────────────────────────────
+
+    /**
+     * Unbounded text ({@code TEXT}).
+     * For length-limited strings use {@link #varChar(int)}.
+     */
+    public static final ColumnType TEXT = new ColumnType("TEXT");
+
+    /** Small text up to 255 characters ({@code TINYTEXT}). MySQL / MariaDB only. */
+    public static final ColumnType TINYTEXT = new ColumnType("TINYTEXT");
+
+    /** Medium text up to 16 MB ({@code MEDIUMTEXT}). MySQL / MariaDB only. */
+    public static final ColumnType MEDIUMTEXT = new ColumnType("MEDIUMTEXT");
+
+    /** Large text up to 4 GB ({@code LONGTEXT}). MySQL / MariaDB only. */
+    public static final ColumnType LONGTEXT = new ColumnType("LONGTEXT");
+
+    /** Character large object ({@code CLOB}). Standard SQL; map to TEXT on MySQL. */
+    public static final ColumnType CLOB = new ColumnType("CLOB");
+
+    // ── Binary types ───────────────────────────────────────────────────────
+
+    /** Binary large object ({@code BLOB}). */
+    public static final ColumnType BLOB = new ColumnType("BLOB");
+
+    /** Small binary up to 255 bytes ({@code TINYBLOB}). MySQL / MariaDB only. */
+    public static final ColumnType TINYBLOB = new ColumnType("TINYBLOB");
+
+    /** Medium binary up to 16 MB ({@code MEDIUMBLOB}). MySQL / MariaDB only. */
+    public static final ColumnType MEDIUMBLOB = new ColumnType("MEDIUMBLOB");
+
+    /** Large binary up to 4 GB ({@code LONGBLOB}). MySQL / MariaDB only. */
+    public static final ColumnType LONGBLOB = new ColumnType("LONGBLOB");
+
+    // ── Date and time types ────────────────────────────────────────────────
+
+    /** Calendar date without time-of-day ({@code DATE}). */
+    public static final ColumnType DATE = new ColumnType("DATE");
+
+    /** Time-of-day without date ({@code TIME}). */
+    public static final ColumnType TIME = new ColumnType("TIME");
+
+    /** Date and time without timezone ({@code DATETIME}). MySQL / MariaDB / SQLite. */
+    public static final ColumnType DATETIME = new ColumnType("DATETIME");
+
+    /** Date and time, often auto-updated ({@code TIMESTAMP}). */
+    public static final ColumnType TIMESTAMP = new ColumnType("TIMESTAMP");
+
+    // ── Miscellaneous types ────────────────────────────────────────────────
+
+    /** JSON document ({@code JSON}). MySQL 5.7+, PostgreSQL 9.2+, SQLite 3.38+. */
+    public static final ColumnType JSON = new ColumnType("JSON");
+
+    /**
+     * Auto-incrementing 4-byte integer ({@code SERIAL}).
+     * PostgreSQL only; equivalent to {@code INT NOT NULL AUTO_INCREMENT} on MySQL.
+     */
+    public static final ColumnType SERIAL = new ColumnType("SERIAL");
+
+    /**
+     * Auto-incrementing 8-byte integer ({@code BIGSERIAL}).
+     * PostgreSQL only; equivalent to {@code BIGINT NOT NULL AUTO_INCREMENT} on MySQL.
+     */
+    public static final ColumnType BIGSERIAL = new ColumnType("BIGSERIAL");
+
+    /**
+     * Universally unique identifier ({@code UUID}).
+     * Native on PostgreSQL; stored as {@code CHAR(36)} or {@code BINARY(16)} on others.
+     */
+    public static final ColumnType UUID = new ColumnType("UUID");
+
+    // ── Internal state ─────────────────────────────────────────────────────
+
+    /** The SQL fragment representing this column type definition. */
+    private final String sql;
+
+    /**
+     * Creates a {@code ColumnType} from an arbitrary SQL type fragment.
+     *
+     * <p>Use this constructor for database-specific types not covered by the
+     * pre-defined constants, e.g. {@code new ColumnType("GEOMETRY")}.</p>
+     *
+     * @param sql the SQL type string; must not be {@code null} or blank
+     */
+    public ColumnType(final String sql) {
+        this.sql = sql;
+    }
+
+    // ── Parameterised factory methods ──────────────────────────────────────
+
+    /**
+     * Variable-length character string: {@code VARCHAR(length)}.
+     *
+     * @param length maximum number of characters; must be positive
+     * @return a new {@code ColumnType} representing {@code VARCHAR(length)}
+     */
+    public static ColumnType varChar(final int length) {
+        return new ColumnType("VARCHAR(" + length + ")");
+    }
+
+    /**
+     * Fixed-length character string: {@code CHAR(length)}.
+     *
+     * @param length number of characters; must be positive
+     * @return a new {@code ColumnType} representing {@code CHAR(length)}
+     */
+    public static ColumnType charType(final int length) {
+        return new ColumnType("CHAR(" + length + ")");
+    }
+
+    /**
+     * Exact decimal number: {@code DECIMAL(precision, scale)}.
+     *
+     * @param precision total number of significant digits; must be positive
+     * @param scale     number of digits after the decimal point; must be &ge; 0
+     * @return a new {@code ColumnType} representing {@code DECIMAL(precision, scale)}
+     */
+    public static ColumnType decimal(final int precision, final int scale) {
+        return new ColumnType("DECIMAL(" + precision + ", " + scale + ")");
+    }
+
+    /**
+     * Exact numeric value: {@code NUMERIC(precision, scale)}.
+     * Equivalent to {@link #decimal(int, int)} in most databases.
+     *
+     * @param precision total number of significant digits; must be positive
+     * @param scale     number of digits after the decimal point; must be &ge; 0
+     * @return a new {@code ColumnType} representing {@code NUMERIC(precision, scale)}
+     */
+    public static ColumnType numeric(final int precision, final int scale) {
+        return new ColumnType("NUMERIC(" + precision + ", " + scale + ")");
+    }
+
+    /**
+     * Fixed-length binary string: {@code BINARY(length)}.
+     *
+     * @param length number of bytes; must be positive
+     * @return a new {@code ColumnType} representing {@code BINARY(length)}
+     */
+    public static ColumnType binary(final int length) {
+        return new ColumnType("BINARY(" + length + ")");
+    }
+
+    /**
+     * Variable-length binary string: {@code VARBINARY(length)}.
+     *
+     * @param length maximum number of bytes; must be positive
+     * @return a new {@code ColumnType} representing {@code VARBINARY(length)}
+     */
+    public static ColumnType varBinary(final int length) {
+        return new ColumnType("VARBINARY(" + length + ")");
+    }
+
+    /**
+     * Timestamp with fractional seconds precision: {@code TIMESTAMP(precision)}.
+     * Useful for {@code TIMESTAMP(6)} (microseconds) on MySQL and PostgreSQL.
+     *
+     * @param precision fractional seconds digits (0–6); must be between 0 and 6 inclusive
+     * @return a new {@code ColumnType} representing {@code TIMESTAMP(precision)}
+     */
+    public static ColumnType timestamp(final int precision) {
+        return new ColumnType("TIMESTAMP(" + precision + ")");
+    }
+
+    // ── Column-level constraint modifiers ──────────────────────────────────
+
+    /**
+     * Appends {@code NOT NULL} to this column type.
+     *
+     * @return a new {@code ColumnType} with {@code NOT NULL} appended
+     */
+    public ColumnType notNull() {
+        return new ColumnType(sql + " NOT NULL");
+    }
+
+    /**
+     * Appends {@code UNIQUE} to this column type.
+     *
+     * @return a new {@code ColumnType} with {@code UNIQUE} appended
+     */
+    public ColumnType unique() {
+        return new ColumnType(sql + " UNIQUE");
+    }
+
+    /**
+     * Appends {@code AUTO_INCREMENT} to this column type (MySQL / MariaDB).
+     * Use {@link #SERIAL} or {@link #BIGSERIAL} for PostgreSQL auto-increment columns.
+     *
+     * @return a new {@code ColumnType} with {@code AUTO_INCREMENT} appended
+     */
+    public ColumnType autoIncrement() {
+        return new ColumnType(sql + " AUTO_INCREMENT");
+    }
+
+    /**
+     * Appends {@code DEFAULT value} to this column type.
+     *
+     * <p>The {@code value} string is inserted verbatim into the SQL column definition.
+     * Use only static, known-safe values here (e.g. {@code "0"}, {@code "false"},
+     * {@code "CURRENT_TIMESTAMP"}). Never pass user-supplied input.</p>
+     *
+     * @param value the default SQL expression or literal to append; must not be {@code null}
+     * @return a new {@code ColumnType} with {@code DEFAULT value} appended
+     */
+    public ColumnType defaultValue(final String value) {
+        return new ColumnType(sql + " DEFAULT " + value);
+    }
+
+    // ── Accessors ──────────────────────────────────────────────────────────
+
+    /**
+     * Returns the SQL fragment for this column type, including any modifiers.
+     *
+     * @return the SQL column type string (e.g. {@code "VARCHAR(64) NOT NULL"})
+     */
+    public String toSql() {
+        return sql;
+    }
+
+    /**
+     * Returns the SQL fragment for this column type.
+     * Equivalent to {@link #toSql()}.
+     *
+     * @return the SQL column type string
+     */
+    @Override
+    public String toString() {
+        return sql;
+    }
+}

src/main/java/com/github/ezframework/javaquerybuilder/query/builder/CreateBuilder.java

@@ -39,16 +39,37 @@ public CreateBuilder table(String table) {
     }
 
     /**
-     * Adds a column definition.
-     * @param name the column name
-     * @param sqlType the SQL type (e.g. "VARCHAR(255)", "INT")
-     * @return this builder
+     * Adds a column definition using a raw SQL type string.
+     *
+     * @param name    the column name
+     * @param sqlType the SQL type string (e.g. {@code "VARCHAR(255)"}, {@code "INT NOT NULL"})
+     * @return this builder instance for chaining
      */
-    public CreateBuilder column(String name, String sqlType) {
+    public CreateBuilder column(final String name, final String sqlType) {
         columns.put(name, sqlType);
         return this;
     }
 
+    /**
+     * Adds a column definition using a type-safe {@link ColumnType}.
+     *
+     * <p>Example:</p>
+     * <pre>{@code
+     * QueryBuilder.createTable("users")
+     *     .column("id",       ColumnType.INT.notNull().autoIncrement())
+     *     .column("username", ColumnType.varChar(64).notNull())
+     *     .primaryKey("id")
+     *     .build();
+     * }</pre>
+     *
+     * @param name       the column name
+     * @param columnType the column type; must not be {@code null}
+     * @return this builder instance for chaining
+     */
+    public CreateBuilder column(final String name, final ColumnType columnType) {
+        return column(name, columnType.toSql());
+    }
+
     /**
      * Adds a primary key column.
      * @param name the column name