为 PostgresSQL 重写 Select SQL 查询

Question

我根据这个主题在 PostgreSQL 中创建了这些表：

Database design for user settings

-- TABLE SETTING

CREATE TABLE SETTING(
 ID INTEGER NOT NULL,
 DESCRIPTION TEXT,
 CONSTRAINED TEXT,
 DATA_TYPE TEXT,
 MIN_VALUE TEXT,
 MAX_VALUE TEXT
)
;

-- ADD KEYS FOR TABLE SETTING

ALTER TABLE SETTING ADD CONSTRAINT KEY34 PRIMARY KEY (ID)
;

-- TABLE ALLOWED_SETTING_VALUE

CREATE TABLE ALLOWED_SETTING_VALUE(
 ID INTEGER NOT NULL,
 SETTING_ID INTEGER,
 ITEM_VALUE TEXT,
 CAPTION TEXT
)
;

-- CREATE INDEXES FOR TABLE ALLOWED_SETTING_VALUE

CREATE INDEX IX_RELATIONSHIP16 ON ALLOWED_SETTING_VALUE (SETTING_ID)
;

-- ADD KEYS FOR TABLE ALLOWED_SETTING_VALUE

ALTER TABLE ALLOWED_SETTING_VALUE ADD CONSTRAINT KEY35 PRIMARY KEY (ID)
;

-- TABLE USER_SETTING

CREATE TABLE USER_SETTING(
 ID INTEGER NOT NULL,
 USER_ID INTEGER,
 SETTING_ID INTEGER,
 ALLOWED_SETTING_VALUE_ID INTEGER,
 UNCONSTRAINED_VALUE TEXT
)
;

-- CREATE INDEXES FOR TABLE USER_SETTING

CREATE INDEX IX_RELATIONSHIP15 ON USER_SETTING (SETTING_ID)
;

CREATE INDEX IX_RELATIONSHIP17 ON USER_SETTING (ALLOWED_SETTING_VALUE_ID)
;

-- ADD KEYS FOR TABLE USER_SETTING

ALTER TABLE USER_SETTING ADD CONSTRAINT KEY36 PRIMARY KEY (ID)
;

但是当我运行 Select SQL 查询时我得到错误，因为它是针对 MySQL:

-- Show settings for a given user
select
  US.user_id 
, S1.description 
, S1.data_type 
, case when S1.constrained = 'true'
  then AV.item_value
  else US.unconstrained_value
  end value
, AV.caption
from USER_SETTING US
  inner join SETTING S1
    on US.setting_id = S1.id 
  left outer join ALLOWED_SETTING_VALUE AV
    on US.allowed_setting_value_id = AV.id
where US.user_id = 234

结果

ERROR:  syntax error at or near "value"
LINE 8:   end value

我如何为 PostgreSQL 重写此 SQL 查询？

Answer 1

value为保留关键字，需要在SQL:

中引用

case when S1.constrained = 'true'
    then AV.item_value
    else US.unconstrained_value
end "value"

添加 as 关键字有效，因为这消除了 value 可能是什么的歧义。但最好还是引用它 - 即使在使用 as 关键字（或查找不同的名称）时也是如此。

This behaviour is documented 并且手册明确提到关键字 value

The AS keyword is optional, but only if the new column name does not match any PostgreSQL keyword (see Appendix C). To avoid an accidental match to a keyword, you can double-quote the column name. For example, VALUE is a keyword, so this does not work:

SELECT a value, b + c AS sum FROM ...

but this does:

SELECT a "value", b + c AS sum FROM ...

For protection against possible future keyword additions, it is recommended that you always either write AS or double-quote the output column name.

无关，但是：

您不应在 text 列中存储布尔值（true、false）。为此，Postgres 有一个原生的 boolean 数据类型。

为 PostgresSQL 重写 Select SQL 查询

Rewrite Select SQL query for PostgreSQL

sql

postgresql

postgresql-9.1

postgresql-9.3