sql92 select 语法 说明
SQL92 SELECT Syntax Description
The SQL92 standard defines the SELECT statement for querying data from a relational database. Below is a description of its syntax:
1.SELECT Clause: The SELECT clause specifies the columns to be retrieved from the database table. It begins with the keyword SELECT followed by a comma-separated list of column names or expressions. For example:
SELECT column1, column2, ...
2.FROM Clause: The FROM clause specifies the table or tables from which to retrieve the data. It follows the SELECT clause and includes the keyword FROM followed by the table name or a list of tables joined together. For example:
FROM table_name
3.WHERE Clause (Optional): The WHERE clause filters the rows returned by the SELECT statement based on specified conditions. It follows the FROM clause and includes the keyword WHERE followed by one or more conditions. For example:
WHERE condition
4.GROUP BY Clause (Optional): The GROUP BY clause is used to group the result set by one or more columns. It follows the WHERE clause (if present) and includes the keyword GROUP BY followed by a list of columns. For example:
GROUP BY column1, column2, ...
5.HAVING Clause (Optional): The HAVING clause filters the grouped rows based on specified conditions. It follows the GROUP BY clause (if present) and includes the keyword HAVING followed by one or more conditions. For example:
HAVING condition
6.ORDER BY Clause (Optional): The ORDER BY clause is used to sort the result set by one or more columns. It follows the HAVING clause (if present) and includes the keyword ORDER BY followed by a list of columns and sorting directions (ASC for ascending, DESC for descending). For example:
ORDER BY column1 ASC, column2 DESC
7.LIMIT Clause (Optional): The LIMIT clause is used to limit the number of rows returned by the SELECT statement. It follows the ORDER BY clause (if present) and includes the keyword LIMIT followed by the maximum number of rows to return. For example:
LIMIT 10
中文描述：
SQL92 SELECT 语法描述
SQL92 标准定义了用于从关系数据库中查询数据的 SELECT 语句。以下是其语法描述：
1.SELECT 子句：SELECT 子句指定要从数据库表中检索的列。它以 SELECT 关键字开头，后面跟着一个用逗号分隔的列名或表达式列表。例如：
SELECT column1, column2, ...
2.FROM 子句：FROM 子句指定要从中检索数据的表。它跟在 SELECT 子句之后，包括 FROM 关键字，后面跟着表名或连接在一起的表列表。例如：
FROM table_name
3.WHERE 子句（可选）：WHERE 子句根据指定的条件过滤 SELECT 语句返回的行。它跟在 FROM 子句之后，包括 WHERE 关键字，后面跟着一个或多个条件。例如：
WHERE condition
4.GROUP BY 子句（可选）：GROUP BY 子句用于根据一个或多个列对结果集进行分组。它跟在 WHERE 子句之后（如果有的话），包括 GROUP BY 关键字，后面跟着一个列的列表。例如：
GROUP BY column1, column2, ...
5.HAVING 子句（可选）：HAVING 子句根据指定的条件过滤分组的行。它跟在 GROUP BY 子句之后（如果有的话），包括 HAVING 关键字，后面跟着一个或多个条件。例如：
HAVING condition
6.ORDER BY 子句（可选）：ORDER BY 子句用于按一个或多个列对结果集进行排序。它跟在 HAVING 子句之后（如果有的话），包括 ORDER BY 关键字，后面跟着一个列和排序方向（ASC 表示升序，DESC 表示降序）的列表。例如：
ORDER BY column1 ASC, column2 DESC
queryselectorall用法
7.LIMIT 子句（可选）：LIMIT 子句用于限制 SELECT 语句返回的行数。它跟在 ORDER BY 子句之后（如果有的话），包括 LIMIT 关键字，后面跟着要返回的最大行数。例如：
LIMIT 10

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