SQL通过列号/索引/位置而不是列名选择列

Question

How to query select column via column number/index/position instead of column name?

So far this does not work:

SELECT 1,2,3,4,5,6,7 from table_1
Union 
SELECT 1,2,3,4,5,6,7 from table_2

Answer 1

If the DB supports common table expressions (all except MySQL), you can give the columns new names:

WITH cte(c1, c2, c3, c4, c5, c6, c7) AS (
    SELECT * FROM table_1
    UNION
    SELECT * FROM table_2
)
SELECT c1, c2, c3, c4, c5, c6, c7 FROM cte;

However, this works only if you can use SELECT * , so both tables must have the same, known number of columns.

In MySQL, you could use a view with column names instead:

CREATE VIEW v(c1, c2, c3, c4, c5, c6, c7) AS SELECT ...;

Answer 2

I don't know which dbms you are using but I'm pretty sure it can't be done, and even if it is possible, I would not recommend that at all. That won't save you a lot of time and I'm guessing its just comes from laziness , but in the future if someone would work on your work, he won't understand a thing. In addition, if you'll need to change one of the columns/drop or add you are leading your self into an mess. My suggestion - Use the full name

Answer 3

Just UNION the SELECTS. UNION already acts the way you want. It ignores column names in unioning rows then uses the column names from the first argument as column names for the result.

SELECT * from table_1
Union 
SELECT * from table_2

MySQL 5.7 Reference Manual 13.2.9.3 UNION Syntax

The column names from the first SELECT statement are used as the column names for the results returned. Selected columns listed in corresponding positions of each SELECT statement should have the same data type. (For example, the first column selected by the first statement should have the same type as the first column selected by the other statements.)

Standard SQL has UNION CORRESPONDING that reorders the columns of the second table to be in the same (specified) order.