获取所有具有当前值的序列

Question

我有以下获取所有序列及其模式的查询：

SELECT sequence_schema as schema, sequence_name as sequence
FROM information_schema.sequences
WHERE sequence_schema NOT IN ('topology', 'tiger')
ORDER BY 1, 2

我想用 select last_value from [sequence]; 之类的东西获取每个序列名称的当前值。我尝试了以下方法（以及一些变体），但它不起作用，因为语法不正确：

DO $$
BEGIN
    EXECUTE 
        sequence_schema as schema,
        sequence_name as sequence,
        last_value
    FROM information_schema.sequences
    LEFT JOIN (
        EXECUTE 'SELECT last_value FROM ' || schema || '.' || sequence
    ) tmp
    ORDER BY 1, 2;
END
$$;

我找到了一些创建函数来执行文本或在函数内拼凑查询和 return 结果的解决方案，但我更希望有一个我可以运行随心所欲地修改。

Answer 1

你可以依赖函数pg_sequence_last_value

SELECT nspname as schema, 
       relname AS sequence_name,
       coalesce(pg_sequence_last_value(s.oid), 0) AS seq_last_value
FROM pg_class AS s
   JOIN pg_depend AS d ON d.objid = s.oid
   JOIN pg_attribute a ON d.refobjid = a.attrelid
                          AND d.refobjsubid = a.attnum
   JOIN pg_namespace nsp ON s.relnamespace = nsp.oid
WHERE s.relkind = 'S'
  AND d.refclassid = 'pg_class'::regclass
  AND d.classid = 'pg_class'::regclass
  AND nspname NOT IN ('topology', 'tiger')
ORDER BY 1,2 DESC;

Answer 2

在 Postgres 12 中，您可以使用 pg_sequences:

select schemaname as schema, 
       sequencename as sequence, 
       last_value
from pg_sequences

Answer 3

这是一个不依赖于 pg_sequences 或 pg_sequence_last_value 的解决方案：

    CREATE OR REPLACE FUNCTION get_sequences()
      RETURNS TABLE (
        last_value bigint,
        sequence_schema text,
        sequence_name text
      )
      LANGUAGE plpgsql AS
    $func$
    DECLARE
        s RECORD;
    BEGIN
        FOR s IN SELECT t.sequence_schema, t.sequence_name
               FROM information_schema.sequences t
        LOOP
          RETURN QUERY EXECUTE format(
              'SELECT last_value, ''%1$s''::text, ''%2$s''::text FROM %1$I.%2$I',
              s.sequence_schema,
              s.sequence_name
          );
        END LOOP;
    END;
    $func$;

    SELECT * FROM get_sequences();

这将输出一个 table 像这样：

 last_value | sequence_schema |                     sequence_name
------------+-----------------+-------------------------------------------------------
          1 | public          | contact_infos_id_seq
          1 | media           | photos_id_seq
       2006 | company         | companies_id_seq
       2505 | public          | houses_id_seq
          1 | public          | purchase_numbers_id_seq
... etc

其他答案只有在您使用现代版本的 Postgres（我相信 10 或更高版本）时才有效。

获取所有具有当前值的序列

Get all sequences with current values

postgresql

sequence

postgresql-12