mysql> create tabletest1(a int notnullcomment'字段a',bvarchar(10) notnulldefault''comment'字段b');QueryOK,0rows affected (0.01sec) mysql> insert into test1values(1,'a'),(2,'b'),(3,'c');QueryOK,3rows affected (0.01sec)Records:3Duplicates:0Warnings:0mysql> select a,bfromtest1; +...
此外,子查询(包括FROM子句中的子查询)和第一个SELECT以外的UNION中的SELECT语句不允许使用这些修饰符。 对于视图,如果SQL_NO_CACHE出现在查询中的任何SELECT中,则适用 For a cacheable query, SQL_CACHE applies if it appears in the first SELECT of a view referred to by the query. 从MySQL 5.7.20开始,...
mysql> select a as 列1,b as 列 2 from test1; ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '2 from test1' at line 1 mysql> select a as 列1,b as '列 2' from test1;...
2.3、查询缓存 如果查询语句(select 语句),MySQL 就会先去查询缓存( Query Cache )里查找缓存数据,看看之前有没有执行过这一条命令,这个查询缓存是以 key-value 形式保存在内存中的,key 为 SQL 查询语句的哈希值,value 为 SQL 语句查询的结果。 如果查询的语句命中查询缓存,那么就会直接返回 value 给客户端。如...
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select * from user where userid=1; 即查询user表中userid为1的用户。 连接器 负责与客户端建立连接、获取权限、维持和管理连接。 输入连接命令 mysql -u root -p 虽然密码也可直接跟在-p后,但这样可能密码泄露。生产服务器建议不要这么做。 连接命令中的mysql是客户端工具,用来跟服务端建立连接。
CREATEPROCEDUREProc()BEGINSELECT*FROMt3;ENDQuery:CREATEPROCEDUREProc()BEGINSELECT*FROMt3 Error Code:1064You have an errorinyourSQLsyntax;check the manual that corresponds to your MySQL server versionforthe right syntax to use near''at line3Execution Time:0sec ...
SELECT语句的执行流程: 1. 2. 3. FROM clause —> WHERE clause —->GROUP BY —-> HAVING clause —->ORDER BY —->SELECT —-> LIMIT SELECT语句 DISTINCT:指定的结果相同的显示一次 SQL_CACHE:缓存于查询缓存中。 SQL_NO_CACHE:不缓存查询结果 ...
PROCEDUREsyntax is deprecated as of MySQL 5.7.18, and is removed in MySQL 8.0. TheSELECT ... INTOform ofSELECTenables the query result to be written to a file or stored in variables. For more information, seeSection 13.2.9.1, “SELECT ... INTO Statement”. ...