问题
I have a PostgreSQL database table with 4 columns - labeled column_a, column_b, etc. I want to query this table with a simple select query:
select * from table_name;
I get a handful of results looking like:
column_a | column_b
---------+---------
'a value'|'b_value'
But when I use this query:
select * from schema_name.table_name;
I get the full result:
column_a | column_b | column_c | column_d
---------+----------+----------+---------
'a value'|'b value' |'c value' |'d_value'
Columns c and d were added at a later date, after initial table creation. My question is: Why would the database ignore the later columns when the schema name is left out of the select query?
回答1:
Table names are not unique within a database in Postgres. There can be any number of tables named 'table_name' in different schemas - including the temporary schema, which always comes first unless you explicitly list it after other schemas in the search_path. Obviously, there are multiple tables named table_name. You must understand the role of the search_path to interpret this correctly:
- How does the search_path influence identifier resolution and the "current schema"
The first table lives in a schema that comes before schema_name in your search_path (or schema_name is not listed there at all). So the unqualified table name is resolved to this table (or view). Check the list of tables named 'table_name' that your current role has access to in your database:
SELECT *
FROM information_schema.tables
WHERE table_name = 'table_name';
Views are just special tables with an attached RULE internally. They could play the same role as a regular table and are included in the above query.
Details:
- How to check if a table exists in a given schema
来源：https://stackoverflow.com/questions/30179061/why-does-a-postgresql-select-query-return-different-results-when-a-schema-name-i