Create table with character set in mysql

10.3.4 Table Character Set and Collation

Every table has a table character set and a table collation. The CREATE TABLE and ALTER TABLE statements have optional clauses for specifying the table character set and collation:

CREATE TABLE tbl_name (column_list)
    [[DEFAULT] CHARACTER SET charset_name]
    [COLLATE collation_name]]

ALTER TABLE tbl_name
    [[DEFAULT] CHARACTER SET charset_name]
    [COLLATE collation_name]

Example:

CREATE TABLE t1 ( ... )
CHARACTER SET latin1 COLLATE latin1_danish_ci;

MySQL chooses the table character set and collation in the following manner:

• If both CHARACTER SET charset_name and COLLATE collation_name are specified, character set charset_name and collation collation_name are used.

• If CHARACTER SET charset_name is specified without COLLATE, character set charset_name and its default collation are used. To see the default collation for each character set, use the SHOW CHARACTER SET statement or query the INFORMATION_SCHEMA CHARACTER_SETS table.

• If COLLATE collation_name is specified without CHARACTER SET, the character set associated with collation_name and collation collation_name are used.

• Otherwise (neither CHARACTER SET nor COLLATE is specified), the database character set and collation are used.

The table character set and collation are used as default values for column definitions if the column character set and collation are not specified in individual column definitions. The table character set and collation are MySQL extensions; there are no such things in standard SQL.

10.3.9 Examples of Character Set and Collation Assignment

The following examples show how MySQL determines default character set and collation values.

Example 1: Table and Column Definition

CREATE TABLE t1
(
    c1 CHAR(10) CHARACTER SET latin1 COLLATE latin1_german1_ci
) DEFAULT CHARACTER SET latin2 COLLATE latin2_bin;

Here we have a column with a latin1 character set and a latin1_german1_ci collation. The definition is explicit, so that is straightforward. Notice that there is no problem with storing a latin1 column in a latin2 table.

Example 2: Table and Column Definition

CREATE TABLE t1
(
    c1 CHAR(10) CHARACTER SET latin1
) DEFAULT CHARACTER SET latin1 COLLATE latin1_danish_ci;

This time we have a column with a latin1 character set and a default collation. Although it might seem natural, the default collation is not taken from the table level. Instead, because the default collation for latin1 is always latin1_swedish_ci, column c1 has a collation of latin1_swedish_ci (not latin1_danish_ci).

Example 3: Table and Column Definition

CREATE TABLE t1
(
    c1 CHAR(10)
) DEFAULT CHARACTER SET latin1 COLLATE latin1_danish_ci;

We have a column with a default character set and a default collation. In this circumstance, MySQL checks the table level to determine the column character set and collation. Consequently, the character set for column c1 is latin1 and its collation is latin1_danish_ci.

Example 4: Database, Table, and Column Definition

CREATE DATABASE d1
    DEFAULT CHARACTER SET latin2 COLLATE latin2_czech_ci;
USE d1;
CREATE TABLE t1
(
    c1 CHAR(10)
);

We create a column without specifying its character set and collation. We're also not specifying a character set and a collation at the table level. In this circumstance, MySQL checks the database level to determine the table settings, which thereafter become the column settings.) Consequently, the character set for column c1 is latin2 and its collation is latin2_czech_ci.

10.3.5 Column Character Set and Collation

Every “character” column (that is, a column of type CHAR, VARCHAR, a TEXT type, or any synonym) has a column character set and a column collation. Column definition syntax for CREATE TABLE and ALTER TABLE has optional clauses for specifying the column character set and collation:

col_name {CHAR | VARCHAR | TEXT} (col_length)
    [CHARACTER SET charset_name]
    [COLLATE collation_name]

These clauses can also be used for ENUM and SET columns:

col_name {ENUM | SET} (val_list)
    [CHARACTER SET charset_name]
    [COLLATE collation_name]

Examples:

CREATE TABLE t1
(
    col1 VARCHAR(5)
      CHARACTER SET latin1
      COLLATE latin1_german1_ci
);

ALTER TABLE t1 MODIFY
    col1 VARCHAR(5)
      CHARACTER SET latin1
      COLLATE latin1_swedish_ci;

MySQL chooses the column character set and collation in the following manner:

• If both CHARACTER SET charset_name and COLLATE collation_name are specified, character set charset_name and collation collation_name are used.

  CREATE TABLE t1
  (
      col1 CHAR(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci
  ) CHARACTER SET latin1 COLLATE latin1_bin;

  The character set and collation are specified for the column, so they are used. The column has character set utf8mb4 and collation utf8mb4_unicode_ci.

• If CHARACTER SET charset_name is specified without COLLATE, character set charset_name and its default collation are used.

  CREATE TABLE t1
  (
      col1 CHAR(10) CHARACTER SET utf8mb4
  ) CHARACTER SET latin1 COLLATE latin1_bin;

  The character set is specified for the column, but the collation is not. The column has character set utf8mb4 and the default collation for utf8mb4, which is utf8mb4_0900_ai_ci. To see the default collation for each character set, use the SHOW CHARACTER SET statement or query the INFORMATION_SCHEMA CHARACTER_SETS table.

• If COLLATE collation_name is specified without CHARACTER SET, the character set associated with collation_name and collation collation_name are used.

  CREATE TABLE t1
  (
      col1 CHAR(10) COLLATE utf8mb4_polish_ci
  ) CHARACTER SET latin1 COLLATE latin1_bin;

  The collation is specified for the column, but the character set is not. The column has collation utf8mb4_polish_ci and the character set is the one associated with the collation, which is utf8mb4.

• Otherwise (neither CHARACTER SET nor COLLATE is specified), the table character set and collation are used.

  CREATE TABLE t1
  (
      col1 CHAR(10)
  ) CHARACTER SET latin1 COLLATE latin1_bin;

  Neither the character set nor collation is specified for the column, so the table defaults are used. The column has character set latin1 and collation latin1_bin.

The CHARACTER SET and COLLATE clauses are standard SQL.

If you use ALTER TABLE to convert a column from one character set to another, MySQL attempts to map the data values, but if the character sets are incompatible, there may be data loss.

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