WHERE
WHERE 子句允许通过指定条件过滤数据。
Syntax
sql
SELECT *
FROM table_name
WHERE condition;SELECT *
FROM table_name
WHERE condition;如果有 WHERE 子句，则它必须为布尔类型的表达式，这通常是带有比较和逻辑运算符的表达式。此表达式计算结果为 false 的行将会从进一步的转换或结果中排除。
示例
逻辑运算符
支持 AND、OR 作为逻辑运算符，并可以使用括号（）组合条件。
sql
SELECT * FROM system_metrics
WHERE idc = 'idc0' AND (host = 'host1' OR host = 'host2');SELECT * FROM system_metrics
WHERE idc = 'idc0' AND (host = 'host1' OR host = 'host2');数字
支持 =, !=, >, >=, <, <= 作为比较运算符。
sql
SELECT * FROM system_metrics WHERE cpu_util = 20.0;
SELECT * FROM system_metrics WHERE cpu_util != 20.0;
SELECT * FROM system_metrics WHERE cpu_util > 20.0;
SELECT * FROM system_metrics WHERE cpu_util >= 20.0;
SELECT * FROM system_metrics WHERE cpu_util < 20.0;
SELECT * FROM system_metrics WHERE cpu_util <= 20.0;SELECT * FROM system_metrics WHERE cpu_util = 20.0;
SELECT * FROM system_metrics WHERE cpu_util != 20.0;
SELECT * FROM system_metrics WHERE cpu_util > 20.0;
SELECT * FROM system_metrics WHERE cpu_util >= 20.0;
SELECT * FROM system_metrics WHERE cpu_util < 20.0;
SELECT * FROM system_metrics WHERE cpu_util <= 20.0;List 查找
List 子元素的匹配或不匹配。
List 匹配
sql
SELECT * FROM system_metrics WHERE idc IN ('idc_a', 'idc_b');SELECT * FROM system_metrics WHERE idc IN ('idc_a', 'idc_b');List 不匹配
sql
SELECT * FROM system_metrics WHERE idc NOT IN ('idc_a', 'idc_b');SELECT * FROM system_metrics WHERE idc NOT IN ('idc_a', 'idc_b');