AI代码解释 mysql>create tabletest1(a int notnullcomment'字段a');QueryOK,0rowsaffected(0.01sec)mysql>insert into test1values(null);ERROR1048(23000):Column'a'cannot benullmysql>insert into test1values(1);QueryOK,1rowaffected(0.00sec)mysql>select*from test1;+---+|a|+---+|1|+---+1rowin...
ALTERTABLEuserADDINDEX((MONTH(create_time))); 通过函数索引也可以很方便提高我们的查询效率。具体使用可以查看如下链接 https://dev.mysql.com/doc/refman/8.0/en/create-index.html demo链接 https://github.com/lyb-geek/springboot-learning/tree/master/springboot-mysql-virtual-column...
I have a query with a SELECT statement ... I would love to add a new column with a static value for all records, past and future. So, given this [simple] query ... select a, b, c from table1 ; +---+---+---+ | a | b | c | +---+---+---+ | 1 | 2 | 3 |...
增加表字段:ALTER TABLE tablename ADD [COLUMN] column_definition [FIRST | AFTER col_name] alter table [emp] add column [age] [int(3)]; 删除表字段:ALTER TABLE tablename DROP [COLUMN] col_name 字段改名:ALTER TABLE tablename CHANGE old_col_name column_definition [FIRST|AFTER col_name] 注...
ADDINDEX indexname(column[, ...]) 删除索引 DROPINDEX indexnameONtablename 或: ALTERTABLEtablenameDROPINDEX indexname 创建视图 CREATE[ORREPLACE] [ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}]VIEWviewname [(colname[, ...])] ASselect_statement [WITH[CASCADE|LOCAL]CHECKOPTION] ...
altertable 表名addcolumn 列名称 数据类型; 如:向student表新增加一列stu_height学生身高 altertable studentaddcolumn stu_heightint(11); 删除某一列 altertable 表名dropcolumn 列名称 例如:删除student表中的学生身高 altertable studentdropcolumn stu_height; ...
Column_name:索引列的名称。 Collation:列以什么方式存储在索引中。可以是 A 或 NULL。B+树索引总是 A,即排序的。如果使用了 Heap 存储引擎,并且建立了 Hash 索引,这里就会显示 NULL 了。因为 Hash 根据 Hash 桶存放索引数据,而不是对数据进行排序。
the default value will be looked up from the new system tables and appended before return to server. 6. For the duraton of instant adding column, MDL will be placed and maintained on the table. In this way, we can instantly add a column with full back version compatibility with minimum ...
ALTER TABLE 表名 ADD COLUMN 字段名 字段类型 DEFAULT NULL COMMENT '字段注释' AFTER 字段B名(在这个字段后面插入); 1. 2:根据查询结果的某个字段值,按指定分隔符分割成多行 select a.字段A, substring_index(substring_index(a.字段A, ',', b.help_topic_id + 1), ',', -1) as course ...
set_default_value() : dd::Column, dd::Column_impl set_default_value_null() : dd::Column, dd::Column_impl set_default_value_utf8() : dd::Column, dd::Column_impl set_default_value_utf8_null() : dd::Column, dd::Column_impl set_deferred() : User_var_log_event set_definer() ...