* 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. 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); ...
• 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 cjc.t01 MODIFY COLUMN `ID` varchar(30) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NOT NULL; ALTER TABLE cjc.t01 MODIFY COLUMN `A_CODE` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL; ALTER TABLE cjc.t01 MODIFY COLUMN `B_CODE` varchar...
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. 10. 这种方法比较繁琐,但适用于只有少量表需要添加字段的情况。 2.2 方法二:使用脚本批量添加 可以使用脚本来批量为多个表添加字段。以下是示例...
ALTER TABLE ADD COLUMN <column_name> <column_type> [DEFAULTdefault_value] [FIRST]/[AFTERcolumn_name], ALGORITHM=INSTANT; ALTER TABLE DROP COLUMN <column_name>, ALGORITHM=INSTANT; NOTE : ALGORITHM=INSTANT is optional here as, by default, all ADD/DROP columns are done with ALGORITHM=INSTANT...
SERIAL DEFAULT VALUE is a special case. In the definition of an integer column, it is an alias for NOT NULL AUTO_INCREMENT UNIQUE. Some aspects of explicit DEFAULT clause handling are version dependent【dɪˈpendənt从属物;依靠者;被扶养人:被赡养人:非独立生活的人;】, as described follo...
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...
-- INSTANT ADD COLUMN,TOTAL_ROW_VERSIONS递增1 ALTER TABLE t1 ADD COLUMN C5 CHAR(10) DEFAULT "c5_def", ALGORITHM=INSTANT; INSERT INTO t1 values ("r2c1", "r2c2", "r2c3", "r2c4", "r2c5"); -- 数据二 SELECT NAME, TOTAL_ROW_VERSIONS FROM INFORMATION_SCHEMA.INNODB_TABLES WHERE NAME ...
MySQL8 中文参考(八十五) 22.5.7 监控 X 插件 dev.mysql.com/doc/refman/8.0/en/x-plugin-system-monitoring.html 对于一般的 X 插件监控,请使用其公开的状态变量。参见第 22.5.6.3 节,“X 插件状态变量”。有关专门监视消息压缩效果的信息,请参见 X 插件的连接压缩监控。