* Determine whether this column's has a default value * * @return {@code true} if the default value was provided, or {@code false} otherwise */ boolean hasDefaultValue(); 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 对parseDefaultClause方法改造 protected void parseDefaultClau...
In databases, rows are persisted on disk and for every row, columns' value are stored on disk. Now, if a new column is to be added or an old column is to be dropped from a table, the contents of existing rows should be changed to reflect the correct values of columns present in th...
• Adding a column. This feature is also referred to as “Instant ADD COLUMN”. Limitations apply. • Adding or dropping a virtual column. • Adding or dropping a column default value. • Modifying the definition of an ENUM or SET column. • Changing the index type. • Renaming ...
ALTER TABLE `table2` ADD COLUMN `new_column_name` `data_type` DEFAULT `default_value` COMMENT 'description'; -- 为表3添加字段 ALTER TABLE `table3` ADD COLUMN `new_column_name` `data_type` DEFAULT `default_value` COMMENT 'description'; 复制代码 1. 2. 3. 4. 5. 6. 7. 8. 9. 1...
13.6 Data Type Default Values Data type specifications can have explicit or implicit default values. ADEFAULTvalueclause in a data type specification explicitly indicates a default value for a column. Examples: CREATETABLEt1(iINTDEFAULT-1,cVARCHAR(10)DEFAULT'',priceDOUBLE(16,2)DEFAULT0.00); ...
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci ROW_FORMAT=DYNAMIC; 执行查询语句。 SELECT AAA.* FROM( SELECT @xxx AS _xxx, ( SELECT @xxx := GROUP_CONCAT( A_CODE ) FROM t01 WHEREFIND_IN_SET( B_CODE, @xxx ) ) AS cxxx ...
SET/DROP DEFAULT MODIFY COLUMN Add/drop virtual columns Add columns(non-generated) – 我们称之为即时DDL 你可以在一个语句中指定不止一个即时(instant)操作,这里是一下即时(instant)操作的示例 mysql>CREATE TABLE t1 (a INT, b INT, KEY(b)); ...
columns": [ { "char_length": 11, "collation_id": 33, "column_key": 2, "column_type_utf8": "int", "comment": "", "datetime_precision": 0, "datetime_precision_null": 1, "default_option": "", "default_value": "AAAAAA==", "default_value_null": false, "default_value_utf8...
数据字典(Data Dictionary)中存储了诸多数据库的元数据信息如图1所示,包括基本Database, table, index, column, function, trigger, procedure,privilege等;以及与存储引擎相关的元数据,如InnoDB的tablespace, table_id, index_id等。MySQL-8.0在数据字典上进行了诸多优化,本文将对其进行逐一介绍。
dd::Column::se_private_data::default_null: 标识instant column的默认值是否为NULL,具体过程详见函数dd_add_instant_columns。 dd::Column::se_private_data::default:当instant column的默认值不是NULL时存储具体的默认值,column default value需要从innodb类型byte转换成se_private_data中的char类型,具体过程详见...