Is there way to join two tables in SQL not on you index row without getting rid of null values

问题

I have two tables in SQL that look similar to the following:

Code        Symbol       Value
1203        ABC          10.00
1208        XYZ          12.00
1222        null         9.00
1226        ABC          1.00

and

Symbol       Date
ABC          2020-06-07
XYZ          2020-06-08
QRS          2020-06-10

Currently, I am trying to join them as follows

SELECT a.Code, a.Symbol, a.Value, b.Date
FROM table1 a
LEFT JOIN table2 b ON a.Symbol = b.Symbol

This returns the following output:

Code        Symbol       Value          Date
1203        ABC          10.00          2020-06-07
1208        XYZ          12.00          2020-06-08
1226        ABC          1.00           2020-06-07

However, I would like to still keep all rows from the initial table as such and fill in the missing values as null as such:

Code        Symbol       Value          Date
1203        ABC          10.00          2020-06-07
1208        XYZ          12.00          2020-06-08
1222        null         9.00           null
1226        ABC          1.00           2020-06-07

I know this is likely quite straightforward but I have tried researching it and I think I am having a brain cramp because I can't work my issue correctly to find what I need.

Thanks for the help.

回答1:

Edit: I agree with @Gordon Linoff, you probably have your tables in reverse order. Either flip the tables, or use a RIGHT JOIN instead.

Sounds like you want a LEFT (OUTER) JOIN. For a general overiew, see here.

WITH a AS (
    SELECT *
    FROM (VALUES (1203, 'ABC', 10.00),
                 (1208, 'XYZ', 12.00),
                 (1222, null, 9.00),
                 (1226, 'ABC', 1.00)
         ) as a (code, symbol, value)
), b AS (
    SELECT *
    FROM (VALUES ('ABC', '2020-06-07'::date),
                 ('XYZ', '2020-06-08'::date),
                 ('QRS', '2020-06-10'::date)
         ) as b (symbol, date)
)
SELECT code, a.symbol, value, date
FROM a LEFT JOIN b ON a.symbol = b.symbol

+----+------+-----+----------+
|code|symbol|value|date      |
+----+------+-----+----------+
|1203|ABC   |10   |2020-06-07|
|1208|XYZ   |12   |2020-06-08|
|1222|NULL  |9    |NULL      |
|1226|ABC   |1    |2020-06-07|
+----+------+-----+----------+

来源：https://stackoverflow.com/questions/63493602/is-there-way-to-join-two-tables-in-sql-not-on-you-index-row-without-getting-rid

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