If a default value evaluates to a data type that differs from the declared column type, implicit coercion to the declared type occurs according to the usual MySQL type-conversion rules. See Section 12.3, “Type Conversion in Expression Evaluation” . 

## Explicit Default Handling Prior to MySQL 8.0.13 

With one exception, the default value specified in a DEFAULT  clause must be a literal constant; it cannot be a function or an expression. This means, for example, that you cannot set the default for a date column to be the value of a function such as NOW()  or CURRENT_DATE . The exception is that, for TIMESTAMP  and DATETIME  columns, you can specify CURRENT_TIMESTAMP  as the default. See Section 11.2.5, “Automatic Initialization and Updating for TIMESTAMP and DATETIME” . 

The BLOB , TEXT , GEOMETRY , and JSON  data types cannot be assigned a default value. 

If a default value evaluates to a data type that differs from the declared column type, implicit coercion to the declared type occurs according to the usual MySQL type-conversion rules. See Section 12.3, “Type Conversion in Expression Evaluation” . 

## Implicit Default Handling 

If a data type specification includes no explicit DEFAULT  value, MySQL determines the default value as follows: 

If the column can take NULL  as a value, the column is defined with an explicit DEFAULT NULL  clause. 

If the column cannot take NULL  as a value, MySQL defines the column with no explicit DEFAULT  clause. 

For data entry into a NOT NULL  column that has no explicit DEFAULT  clause, if an INSERT  or REPLACE statement includes no value for the column, or an UPDATE  statement sets the column to NULL , MySQL handles the column according to the SQL mode in effect at the time: 

•If strict SQL mode is enabled, an error occurs for transactional tables and the statement is rolled back. For nontransactional tables, an error occurs, but if this happens for the second or subsequent row of a multiple-row statement, the preceding rows are inserted. 

•If strict mode is not enabled, MySQL sets the column to the implicit default value for the column data type. 

Suppose that a table t  is defined as follows: 

CREATE TABLE t (i INT NOT NULL); 

In this case, i  has no explicit default, so in strict mode each of the following statements produce an error and no row is inserted. When not using strict mode, only the third statement produces an error; the implicit default is inserted for the first two statements, but the third fails because DEFAULT(i)  cannot produce a value: 

INSERT INTO t VALUES(); INSERT INTO t VALUES(DEFAULT); INSERT INTO t VALUES(DEFAULT(i)); 

See Section 5.1.11, “Server SQL Modes” . 

For a given table, the SHOW CREATE TABLE  statement displays which columns have an explicit DEFAULT clause. 

Implicit defaults are defined as follows: 

