UNION RESULT UNION的结果 。 SUBQUERY 子查询中的第一个SELECT语句。 DEPENDENT SUBQUERY 子查询中的第一个SELECT语句,同时该语句依赖外部的查询。 DERIVED 派生表。位于form中的子查询,MySQL会将其结果存放在一个临时表中,即这里的派生表。 MATERIALIZED 物化子查询,优化 FROM/IN 子句中的子查询。 UNCACHEABLE SUB...
union只是将两条select语句的查询结果组合在一起,而join是将两个表建立起关联后再查询。
Append [All |Distinct]saveAppend used with Subquery Scan to implement UNION and UNION ALL queries. Can operate from disk based on virtue of "save". Miscellaneous/Other: HashhashUsed for inner joins and left and right outer joins (provides input to a hash join). The Hash operator creates th...
SQL> REM The custom SQL Profile to be created by this script SQL> REM will affect plans for SQL commands with signature SQL> REM matching the one for SQL Text below. SQL> REM Review SQL Text and adjust accordingly. SQL> REM SQL> REM PARAMETERS SQL> REM None. SQL> REM SQL> REM EXA...
@ mysql-test/r/union.result test result @ mysql-test/t/union.test test case @ sql/sql_union.cc In UNION if we use last SELECT without braces and this SELECT have ORDER BY clause, such clause belongs to global UNION. It is parsed like last SELECT part and used further as 'unit->...
db2look -d db_alias -a -e -m -l -x -f -o db2look.sql 36.创建数据库 db2 create db test1 37.生成定义 db2 -tvf db2look.sql 38.导入数据库所有的数据 db2move db_alias import 39.重组检查 db2 reorgchk 40.重组表tb1 db2 reorg table tb1 ...
union子句的执行计划 最后 目前的困惑在于如果explain给出的结果是有错误的,那之后优化sql语句时可以相信的工具是什么呢…… 查了许久,没有google到mysql做union操作时explain结果不正确的相关案例。 但是在git上发现了类似例子:有人分享了索引失效选择time索引的案例,也是扫描了百万行数据。很可惜的是该例子没有做unio...
Select A point in the query where multiple results are brought together into a single result set. For example, if a query is the union of two different select statements, at the point before the union occurs, the Select icon indicates the points where the select statements finished and the ...
Example 1-4, "EXPLAIN PLAN Output"is an example of the plan table output when using theUTLXPLS.SQLscript. If you have specified a statement identifier, then you can write your own script to query thePLAN_TABLE. For example: Start with ID = 0 and givenSTATEMENT_ID. ...
Structured Query Language used to manipulate the data with help of queries. The SQL uses some operators to throw queries like SELECT uses to selects a data value and shown on the output screen, Where uses for conditions, Group by uses to...