SELECT
Retrieves data from a table.
Syntax
SELECT
[ALL | DISTINCT]
select_expr [[AS] alias], ...
[INTO variable [, ...]]
[EXCLUDE (col_name1 [, col_name2, col_name3, ...] ) ]
[FROM table_references
[AT ...]
[WHERE expr]
[GROUP BY {{col_name | expr | col_alias | col_position}, ...
| extended_grouping_expr}]
[HAVING expr]
[ORDER BY {col_name | expr | col_alias | col_position} [ASC | DESC], [ NULLS { FIRST | LAST }]
[LIMIT row_count]
[OFFSET row_count]
[IGNORE_RESULT]
]
]
提示
numbers(N) – A table for test with the single number column (UInt64) that contains integers from 0 to N-1.
SELECT Clause
SELECT number FROM numbers(3);
+--------+
| number |
+--------+
| 0 |
| 1 |
| 2 |
+--------+
EXCLUDE Parameter
Excludes one or more columns by their names from the result. The parameter is usually used in conjunction with SELECT * ... to exclude a few columns from the result instead of retrieving them all.
SELECT * FROM allemployees ORDER BY id;
---
| id | firstname | lastname | gender |
|----|-----------|----------|--------|
| 1 | Ryan | Tory | M |
| 2 | Oliver | Green | M |
| 3 | Noah | Shuster | M |
| 4 | Lily | McMent | F |
| 5 | Macy | Lee | F |
-- Exclude the column "id" from the result
SELECT * EXCLUDE id FROM allemployees;
---
| firstname | lastname | gender |
|-----------|----------|--------|
| Noah | Shuster | M |
| Ryan | Tory | M |
| Oliver | Green | M |
| Lily | McMent | F |
| Macy | Lee | F |
-- Exclude the columns "id" and "lastname" from the result
SELECT * EXCLUDE (id,lastname) FROM allemployees;
---
| firstname | gender |
|-----------|--------|
| Oliver | M |
| Ryan | M |
| Lily | F |
| Noah | M |
| Macy | F |
FROM Clause
SELECT number FROM numbers(3) AS a;
+--------+
| number |
+--------+
| 0 |
| 1 |
| 2 |
+--------+
AT Clause
The AT clause enables you to query previous versions of your data. For more information, see AT.
WHERE Clause
SELECT number FROM numbers(3) WHERE number > 1;
+--------+
| number |
+--------+
| 2 |
+--------+
GROUP BY Clause
--Group the rows of the result set by column alias
SELECT number%2 as c1, number%3 as c2, MAX(number) FROM numbers(10000) GROUP BY c1, c2;
+------+------+-------------+
| c1 | c2 | MAX(number) |
+------+------+-------------+
| 1 | 2 | 9995 |
| 1 | 1 | 9997 |
| 0 | 2 | 9998 |
| 0 | 1 | 9994 |
| 0 | 0 | 9996 |
| 1 | 0 | 9999 |
+------+------+-------------+
--Group the rows of the result set by column position in the SELECT list
SELECT number%2 as c1, number%3 as c2, MAX(number) FROM numbers(10000) GROUP BY 1, 2;
+------+------+-------------+
| c1 | c2 | MAX(number) |
+------+------+-------------+
| 1 | 2 | 9995 |
| 1 | 1 | 9997 |
| 0 | 2 | 9998 |
| 0 | 1 | 9994 |
| 0 | 0 | 9996 |
| 1 | 0 | 9999 |
+------+------+-------------+
HAVING Clause
SELECT number%2 as c1, number%3 as c2, MAX(number) as max FROM numbers(10000) GROUP BY c1, c2 HAVING max>9996;
+------+------+------+
| c1 | c2 | max |
+------+------+------+
| 1 | 0 | 9999 |
| 1 | 1 | 9997 |
| 0 | 2 | 9998 |
+------+------+------+
ORDER BY Clause
--Sort by column name in ascending order.
SELECT number FROM numbers(5) ORDER BY number ASC;
+--------+
| number |
+--------+
| 0 |
| 1 |
| 2 |
| 3 |
| 4 |
+--------+
--Sort by column name in descending order.
SELECT number FROM numbers(5) ORDER BY number DESC;
+--------+
| number |
+--------+
| 4 |
| 3 |
| 2 |
| 1 |
| 0 |
+--------+
--Sort by column alias.
SELECT number%2 AS c1, number%3 AS c2 FROM numbers(5) ORDER BY c1 ASC, c2 DESC;
+------+------+
| c1 | c2 |
+------+------+
| 0 | 2 |
| 0 | 1 |
| 0 | 0 |
| 1 | 1 |
| 1 | 0 |
+------+------+
--Sort by column position in the SELECT list
SELECT * FROM t1 ORDER BY 2 DESC;
+------+------+
| a | b |
+------+------+
| 2 | 3 |
| 1 | 2 |
+------+------+
SELECT a FROM t1 ORDER BY 1 DESC;
+------+
| a |
+------+
| 2 |
| 1 |
+------+
--Sort with the NULLS FIRST or LAST option.
CREATE TABLE t_null (
number INTEGER
);
INSERT INTO t_null VALUES (1);
INSERT INTO t_null VALUES (2);
INSERT INTO t_null VALUES (3);
INSERT INTO t_null VALUES (NULL);
INSERT INTO t_null VALUES (NULL);
--Databend considers NULL values larger than any non-NULL values.
--The NULL values appear last in the following example that sorts the results in ascending order:
SELECT number FROM t_null order by number ASC;
+--------+
| number |
+--------+
| 1 |
| 2 |
| 3 |
| NULL |
| NULL |
+--------+
-- To make the NULL values appear first in the preceding example, use the NULLS FIRST option:
SELECT number FROM t_null order by number ASC nulls first;
+--------+
| number |
+--------+
| NULL |
| NULL |
| 1 |
| 2 |
| 3 |
+--------+
-- Use the NULLS LAST option to make the NULL values appear last in descending order:
SELECT number FROM t_null order by number DESC nulls last;
+--------+
| number |
+--------+
| 3 |
| 2 |
| 1 |
| NULL |
| NULL |
+--------+
LIMIT Clause
SELECT number FROM numbers(1000000000) LIMIT 1;
+--------+
| number |
+--------+
| 0 |
+--------+
SELECT number FROM numbers(100000) ORDER BY number LIMIT 2 OFFSET 10;
+--------+
| number |
+--------+
| 10 |
| 11 |
+--------+
OFFSET Clause
SELECT number FROM numbers(5) ORDER BY number OFFSET 2;
+--------+
| number |
+--------+
| 2 |
| 3 |
| 4 |
+--------+
IGNORE_RESULT
Do not output the result set.
SELECT number FROM numbers(2);
+--------+
| number |
+--------+
| 0 |
| 1 |
+--------+
mysql> SELECT number FROM numbers(2) IGNORE_RESULT;
-- Empty set
Nested Sub-Selects
SELECT statements can be nested in queries.
SELECT ... [SELECT ...[SELECT [...]]]
SELECT MIN(number) FROM (SELECT number%3 AS number FROM numbers(10)) GROUP BY number%2;
+-------------+
| min(number) |
+-------------+
| 1 |
| 0 |
+-------------+