在检查约束中使用case语句 [英] Using a case statement in a check constraint

问题描述

上周我一直在学习SQL，但是我不确定如何在检查约束中正确添加case语句.有人可以给我指点吗?

i'v been learning SQL for the last week but I am unsure how to correctly add a case statement within a check constraint. Can anybody give me any pointers?

我有下面的成绩表:

CREATE TABLE Grade
(
    salary_grade    char(1) NOT NULL CHECK (salary_grade = UPPER(salary_grade)),
        CONSTRAINT ck_grade_scale CHECK(
        CASE 
            WHEN salary_grade = '[A-D]' 
                THEN salary_scale = 'S1'
            WHEN salary_grade = '[D-G]' 
                THEN salary_scale = 'S2'
        END)

        salary_scale    char(2) DEFAULT 'S1' NOT NULL,

        CONSTRAINT pk_grade PRIMARY KEY (salary_grade),
        CONSTRAINT ck_salary_grade CHECK (REGEXP_LIKE(salary_grade, '[A-G]', 'c')),
        --constraint must be either S1 or S2
        CONSTRAINT ck_salary_scale CHECK (salary_scale IN ('S1', 'S2'))
);

我想检查salary_grade是否在A-D之间，则salary_scale必须为'S1'，或者salary_grade是否在E-G之间，则为'S2'.

I want to check that if the salary_grade is between A-D then the salary_scale must be 'S1' or if the salary_grade is between E-G then it's 'S2'.

我试图对此进行研究并提出后者，但是它不起作用..我是否正确构造了代码?

I have tried to research this and come up with the latter but however it does not work.. have I structured the code correctly?

推荐答案

我认为您可以执行以下操作:

I think you can do the following:

CREATE TABLE Grade
(
  salary_grade    char(1) NOT NULL CHECK (REGEXP_LIKE(salary_grade, '[A-G]', 'c')),
  salary_scale    char(2) DEFAULT 'S1' NOT NULL,
  CONSTRAINT pk_grade PRIMARY KEY (salary_grade),
  CONSTRAINT ck_grade_scale CHECK ( REGEXP_LIKE(salary_grade, '[A-D]', 'c') AND salary_scale = 'S1'
                                 OR REGEXP_LIKE(salary_grade, '[E-G]', 'c') AND salary_scale = 'S2' )
);

请在此处查看SQL Fiddle模式.

您不需要salary_grade上的UPPER()约束，因为正则表达式检查就足够了(您已经在检查以确保它是A和G之间的大写字母).我认为单独对salary_scale的约束也没有必要，因为从逻辑上讲，它将包含在最后一个约束中.

You don't need the UPPER() constraint on salary_grade since the regex check will suffice (you're already checking to make sure it's an uppercase letter between A and G). I don't think the constraint on salary_scale alone is necessary either since it would be contained, logically, in the last constraint.

更新

以下是使用CASE语句的方法:

Here is how you might do it with a CASE statement:

CREATE TABLE Grade
(
  salary_grade    char(1) NOT NULL CHECK (REGEXP_LIKE(salary_grade, '[A-G]', 'c')),
  salary_scale    char(2) DEFAULT 'S1' NOT NULL,  
  CONSTRAINT pk_grade PRIMARY KEY (salary_grade),
  CONSTRAINT ck_grade_scale CHECK ( salary_scale = CASE WHEN REGEXP_LIKE(salary_grade, '[A-D]', 'c') THEN 'S1' ELSE 'S2' END )
);

请在此处查看SQL Fiddle模式.

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