使用子查询更新 postgres 中的表行

Question

使用 postgres 8.4，我的目标是更新现有表：

CREATE TABLE public.dummy
(
  address_id SERIAL,
  addr1 character(40),
  addr2 character(40),
  city character(25),
  state character(2),
  zip character(5),
  customer boolean,
  supplier boolean,
  partner boolean

)
WITH (
  OIDS=FALSE
);

最初我使用插入语句测试了我的查询：

insert into address customer,supplier,partner
SELECT  
    case when cust.addr1 is not null then TRUE else FALSE end customer, 
    case when suppl.addr1 is not null then TRUE else FALSE end supplier,
    case when partn.addr1 is not null then TRUE else FALSE end partner
from (
    SELECT *
        from address) pa
    left outer join cust_original cust
        on (pa.addr1=cust.addr1 and pa.addr2=cust.addr2 and pa.city=cust.city 
            and pa.state=cust.state and substring(cust.zip,1,5) = pa.zip  )
    left outer join supp_original suppl 
        on (pa.addr1=suppl.addr1 and pa.addr2=suppl.addr2 and pa.city=suppl.city 
                and pa.state=suppl.state and pa.zip = substring(suppl.zip,1,5))
    left outer join partner_original partn
        on (pa.addr1=partn.addr1 and pa.addr2=partn.addr2 and pa.city=partn.city
                  and pa.state=partn.state and pa.zip = substring(partn.zip,1,5) )
where pa.address_id = address_id

作为新手，我无法转换为更新语句，即使用 select 语句返回的值更新现有行。 非常感谢任何帮助。

Answer 1

有很多方法可以更新行。

当涉及到UPDATE 使用子查询的行时，您可以使用这些方法中的任何一种。

1. Approach-1 [使用直接表引用]

UPDATE
  <table1>
SET
  customer=<table2>.customer,
  address=<table2>.address,
  partn=<table2>.partn
FROM
  <table2>
WHERE
  <table1>.address_id=<table2>.address_i;

解释：table1 是我们要更新的表，table2 是表，我们将从中获取要替换/更新的值。 我们使用FROM 子句来获取table2 的数据。 WHERE 子句将有助于设置正确的数据映射。

1. 方法 2 [使用子查询]

UPDATE
  <table1>
SET
  customer=subquery.customer,
  address=subquery.address,
  partn=subquery.partn
FROM
  (
    SELECT
      address_id, customer, address, partn
    FROM  /* big hairy SQL */ ...
  ) AS subquery
WHERE
  dummy.address_id=subquery.address_id;

解释：这里我们在FROM子句中使用子查询， 并给它一个别名。这样它就会像桌子一样。

1. 方法 3 [使用多个联接表]

UPDATE
  <table1>
SET
  customer=<table2>.customer,
  address=<table2>.address,
  partn=<table2>.partn
FROM
  <table2> as t2
  JOIN <table3> as t3
  ON
    t2.id = t3.id
WHERE
  <table1>.address_id=<table2>.address_i;

解释：有时我们面临的情况是，表连接是这样的 获取正确的更新数据很重要。为此，Postgres 允许 我们在FROM 子句中加入多个表。

4. 方法 4 [使用 WITH 语句]

• 4.1 [使用简单查询]

WITH subquery AS (
    SELECT
      address_id,
      customer,
      address,
      partn
    FROM
      <table1>;
)
UPDATE <table-X>
SET customer = subquery.customer,
    address  = subquery.address,
    partn    = subquery.partn
FROM subquery
WHERE <table-X>.address_id = subquery.address_id;

• 4.2 [使用复杂 JOIN 查询]

WITH subquery AS (
    SELECT address_id, customer, address, partn
    FROM
      <table1> as t1
    JOIN
      <table2> as t2
    ON
      t1.id = t2.id;
    -- You can build as COMPLEX as this query as per your need.
)
UPDATE <table-X>
SET customer = subquery.customer,
    address  = subquery.address,
    partn    = subquery.partn
FROM subquery
WHERE <table-X>.address_id = subquery.address_id;

说明：从 Postgres 9.1 开始，这个(WITH) 概念已经 介绍。使用它我们可以进行任何复杂的查询并生成 渴望的结果。这里我们使用这种方法来更新表格。

我希望这会有所帮助..?

Answer 2

您正在使用UPDATE FROM 语法。

UPDATE 
  table T1  
SET 
  column1 = T2.column1 
FROM 
  table T2 
  INNER JOIN table T3 USING (column2) 
WHERE 
  T1.column2 = T2.column2;

参考文献

• 此处的代码示例：GROUP BY in UPDATE FROM clause
• And here
• Formal Syntax Specification

Answer 3

@Mayur “4.2 [使用复杂 JOIN 查询]” 与 公用表表达式 (CTE)对我有用。

WITH cte AS (
SELECT e.id, e.postcode
FROM employees e
LEFT JOIN locations lc ON lc.postcode=cte.postcode
WHERE e.id=1
)
UPDATE employee_location SET lat=lc.lat, longitude=lc.longi
FROM cte
WHERE employee_location.id=cte.id;

希望这会有所帮助... :D

Answer 4

如果使用连接没有性能提升，那么我更喜欢公用表表达式 (CTE) 以提高可读性：

WITH subquery AS (
    SELECT address_id, customer, address, partn
    FROM  /* big hairy SQL */ ...
)
UPDATE dummy
SET customer = subquery.customer,
    address  = subquery.address,
    partn    = subquery.partn
FROM subquery
WHERE dummy.address_id = subquery.address_id;

恕我直言，更现代一点。

Answer 5

update json_source_tabcol as d
set isnullable = a.is_Nullable
from information_schema.columns as a 
where a.table_name =d.table_name 
and a.table_schema = d.table_schema 
and a.column_name = d.column_name;

Answer 6

Postgres 允许：

UPDATE dummy
SET customer=subquery.customer,
    address=subquery.address,
    partn=subquery.partn
FROM (SELECT address_id, customer, address, partn
      FROM  /* big hairy SQL */ ...) AS subquery
WHERE dummy.address_id=subquery.address_id;

这种语法不是标准的 SQL，但是对于这种类型的查询来说，它比标准的 SQL 方便得多。我相信甲骨文（至少）接受类似的东西。