In one can just use ROWNUM, without the parentheses.
ROWNUM() returns the current number of accepted rows in the current context. It main purpose is to emulate the . For MariaDB native applications, we recommend the usage of , as it is easier to use and gives more predictable results than the usage of ROWNUM().
The main difference between using LIMIT andROWNUM() to limit the rows in the result is thatLIMIT works on the result set while ROWNUM works on the number of accepted rows (before any ORDER orGROUP BY clauses).
The following queries will return the same results:
While the following may return different results based on in which orders the rows are found:
The recommended way to use ROWNUM to limit the number of returned rows and get predictable results is to have the query in a subquery and test for ROWNUM() in the outer query:
ROWNUM() can be used in the following contexts:
Used in other contexts, ROWNUM() will return 0.
In many cases where ROWNUM() is used, MariaDB will use the same optimizations it uses with .
LIMIT optimization is possible when using ROWNUM in the following manner:
When one is in a top level WHERE clause comparing ROWNUM() with a numerical constant using any of the following expressions:
ROWNUM() < number.
ROWNUM() <= number.
In the above cases, LIMIT optimization can be done in the
following cases:
For the current subquery when the ROWNUM comparison is done on the top level:
For an inner subquery, when the upper level has only a ROWNUM() comparison in the WHERE clause:
When ROWNUM() is used anywhere in a query, the optimization to ignore ORDER BY in subqueries are disabled.
This was done to get the following common Oracle query to work as expected:
By default, MariaDB ignores any ORDER BY in subqueries both because the SQL standard defines results sets in subqueries to be un-ordered and because of performance reasons (especially when using views in subqueries). See "Wrong result with GROUP BY ... WITH ROLLUP" for a discussion of this topic.
While MariaDB tries to emulate Oracle's usage of ROWNUM() as closely as possible, there are cases where the result is different:
When the optimizer finds rows in a different order (because of different storage methods or optimization). This may also happen in Oracle if one adds or deletes an index, in which case the rows may be found in a different order.
Note that usage of ROWNUM() in functions or will use their own context, not the caller's context.
support Oracle syntax: rownum
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ROWNUM()ROWNUM() = 1ROWNUM() can be also be the right argument to the comparison function.
SELECT * FROM t1 LIMIT 10;
SELECT * FROM t1 WHERE ROWNUM() <= 10;SELECT * FROM t1 ORDER BY a LIMIT 10;
SELECT * FROM t1 ORDER BY a WHERE ROWNUM() <= 10;SELECT * FROM (SELECT * FROM t1 ORDER BY a) WHERE ROWNUM() <= 10;INSERT INTO t1 VALUES (1,ROWNUM()),(2,ROWNUM()),(3,ROWNUM());
INSERT INTO t1 VALUES (1),(2) RETURNING a, ROWNUM();
UPDATE t1 SET row_num_column=ROWNUM();
DELETE FROM t1 WHERE a < 10 AND ROWNUM() < 2;
LOAD DATA INFILE 'filename' INTO TABLE t1 fields terminated BY ','
lines terminated BY "\r\n" (a,b) SET c=ROWNUM();SELECT * FROM t1 WHERE ROWNUM() <= 2 AND t1.a > 0SELECT * FROM (SELECT * FROM t1) AS t WHERE ROWNUM() <= 2SELECT * FROM (SELECT * FROM t1 ORDER BY a DESC) AS t WHERE rownum() <= 2;