数据库θ连接
网站编辑2023-07-01 16:13:33280
以下是一个简单的 SQL 查询语句示例：
SELECT *
FROM table_name
WHERE table_name = 'table1'
这将返回所有行在 table_name 列上的 table_name 列值的总和。table_name 列是表名，包含表中所有记录的名称。如果表名和某些列不匹配，将返回错误消息。
如果您需要在一个表中使用多个 table_name 列，您可以使用 WHERE 子句来限制返回的列。例如，以下查询将返回所有列 'table1' 和与它们匹配的 'table_name' 列的总和：
SELECT *
FROM table_name
WHERE table_name = 'table1'
AND table_name = 'table2'
AND table_name = 'table3'
AND table_name = 'table4'
AND table_name = 'table5'
AND table_name = 'table6'
AND table_name = 'table7'
AND table_name = 'table8'
AND table_name = 'table9'
AND table_name = 'table10'
AND table_name = 'table11'
AND table_name = 'table12'
AND table_name = 'table13'
AND table_name = 'table14'
AND table_name = 'table15'
AND table_name = 'table16'
AND table_name = 'table17'
AND table_name = 'table18'
AND table_name = 'table19'
AND table_name = 'table20'
AND table_name = 'table21'
AND table_name = 'table22'
AND table_name = 'table23'
AND table_name = 'table24'
AND table_name = 'table25'
AND table_name = 'table26'
AND table_name = 'table27'
AND table_name = 'table28'
AND table_name = 'table29'
AND table_name = 'table30'
AND table_name = 'table31'
AND table_name = 'table32'
AND table_name = 'table33'
AND table_name = 'table34'
AND table_name = 'table35'
AND table_name = 'table36'
AND table_name = 'table37'
AND table_name = 'table38'
AND table_name = 'table39'
AND table_name = 'table40'
AND table_name = 'table41'
AND table_name = 'table42'
AND table_name = 'table43'
AND table_name = 'table44'
AND table_name = 'table45'
AND table_name = 'table46'
AND table_name = 'table47'
AND table_name = 'table48'
AND table_name = 'table49'
这个查询使用 WHERE 子句来限制返回的列。例如，如果您要按学生列 'tom' 匹配学生表中的学生名字 'tom'，则该查询将返回所有匹配名字的学生和他们的姓名。
请注意
