create table fruits (type text, variety text, price number); create index fruit_type_price on fruits (type, price); insert into fruits values ('apple', 'gala', 2.79); insert into fruits values ('apple', 'fuji', 0.24); insert into fruits values ('apple', 'limbertwig', 2.87); inser...
GROUP BY子句 GROUP BY子句接受查询的结果行,并根据一个或多个数据库列将它们分成单独的组。 当将SELECT与GROUP BY结合使用时,将为GROUP BY字段的每个不同值检索一行。GROUP BY子句在概念上类似于 IRIS扩展%FOREACH,但是GROUP BY操作整个查询,而%FOREACH允许在子填充上选择聚合,而不限制整个查询填充。 例如: 代...
When you write EXISTS in a where clause, you're telling the optimizer that you want the outer query to be run first, using each value to fetch a value from the inner query. In many cases, EXISTS is better because it requires you to specify a join condition, which can invoke an INDEX...
This is a SELECT statement that evaluates to a single value for each result set row. A complex expression that is built by using operators on one or more simple expressions. For more information about expressions, see Expressions (Transact-SQL). Expressions can include the $ROWGUID keyword. ...
This clause implements SQL-driven Flashback, which lets you specify a different system change number or timestamp for each object in the select list. You can also implement session-level Flashback using theDBMS_FLASHBACKpackage. A Flashback Query lets you retrieve a history of changes made to...
带有两个IN参数的Select查询是一种数据库查询语句,用于从数据库中检索满足指定条件的数据。IN参数允许我们指定一个值列表,查询将返回包含这些值的行。 这种查询的语法如下: SELECT * FROM 表名 WHERE 列名 IN (值1, 值2); 其中,表名是要查询的数据库表的名称,列名是要在其中进行匹配的列的名称,值1和值2...
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SQL 语句中有时会使用 IN 关键字,例如 id in (1,2,3)。可以使用 ${ids}方式直接获取值,但这种写法不能防止 SQL 注入,想避免 SQL 注入就需要用#{}的方式,这时就要配合使用 foreach 标签来满足需求。 foreach 可以对数组、Map 或实现了 Iterable 接口(如 List、Set)的对象进行遍历。数组在处理时会转换为...
MySQL permits duplicate column names. That is, there can be more than oneselect_exprwith the same name. This is an extension to standard SQL. Because MySQL also permitsGROUP BYandHAVINGto refer toselect_exprvalues, this can result in an ambiguity: ...
I have a table in which people have more than one record (they tend to be duplicates) and need to select only one record for each person. This could be done...