Postgres PL/pgSQL 合并存在于各种表中的列

Question

我正在实施一个工具来清理名为 stage 的架构中各个表中的所有客户名称。客户名称可能来自 billing_acc_name 或 cust_acc_names 列。我事先不知道有多少表有这些列，但只要有，它们就会成为清理的一部分。

但是，在清理之前，我需要 select 架构中所有表的所有唯一客户名称。

为了更好地分离关注点，我正在考虑在 PL/pgSQL 中实现它。目前，这就是我在 Python/pandas/SQLAlchemy 等

中实现的方式

table_name = 'information_schema.columns'
table_schema_src = 'stage'
cols = ['billing_acc_name', 'cust_acc_name']

# get list of all table names and column names to query in stage schema
sql = text(f""" 
    SELECT table_name, column_name FROM {table_name} WHERE table_schema ='{table_schema_src}'
    AND column_name = ANY(ARRAY{cols})
""")
src = pd.read_sql(sql, con=engine)

# explore implementation in pgsql
# establish query string
cnames = []
for i, row in src.iterrows():
    s = text(f"""
        SELECT DISTINCT upper({row['column_name']}) AS cname FROM stage.{row['table_name']}
    """)
    cnames.append(str(s).strip())

sql = ' UNION '.join(cnames)

df = pd.read_sql(sql, con=engine)

自动生成的SQL查询字符串如下：

SELECT DISTINCT upper(cust_acc_name) AS cname FROM stage.journal_2017_companyA UNION 
SELECT DISTINCT upper(billing_acc_name) AS cname FROM stage.journal_2017_companyA UNION 
SELECT DISTINCT upper(cust_acc_name) AS cname FROM stage.journal_2017_companyB UNION 
SELECT DISTINCT upper(billing_acc_name) AS cname FROM stage.journal_2017_companyB UNION 
SELECT DISTINCT upper(cust_acc_name) AS cname FROM stage.journal_2017_companyC UNION 
SELECT DISTINCT upper(billing_acc_name) AS cname FROM stage.journal_2017_companyC UNION 
SELECT DISTINCT upper(cust_acc_name) AS cname FROM stage.journal_2017_companyD UNION 
SELECT DISTINCT upper(billing_acc_name) AS cname FROM stage.journal_2017_companyD

Answer 1

plpgsql 函数可能如下所示：

create or replace function select_acc_names(_schema text)
returns setof text language plpgsql as $$
declare
    rec record;
begin
    for rec in
        select table_name, column_name
        from information_schema.columns
        where table_schema = _schema
        and column_name = any(array['cust_acc_name', 'billing_acc_name'])
    loop
        return query
        execute format ($fmt$
            select upper(%I) as cname
            from %I.%I
            $fmt$, rec.column_name, _schema, rec.table_name);
    end loop;
end $$;

使用：

select *
from select_acc_names('stage');

Postgres PL/pgSQL 合并存在于各种表中的列

Postgres PL/pgSQL To Consolidate Columns Existing Across Various Tables

sql

postgresql

plpgsql