mysql – 使用SQL查询打印Prime数字

我是StackOverflow的新手,并且遇到了一个查询,打印从2到1000的素数.
我使用了以下查询需要输入,如果这是最有效的编码方式.

WITH NUM AS (
    SELECT LEVEL N 
    FROM DUAL CONNECT BY LEVEL <= 1000
) 
SELECT LISTAGG(B.N,'-') WITHIN GROUP(ORDER BY B.N) AS PRIMES 
FROM (
    SELECT  N,
            CASE WHEN EXISTS (
                                SELECT NULL 
                                FROM NUM N_INNER 
                                WHERE N_INNER .N > 1 
                                AND N_INNER.N < NUM.N 
                                AND MOD(NUM.N, N_INNER.N)=0
                            ) THEN 
                'NO PRIME' 
            ELSE 
                'PRIME' 
            END IS_PRIME 
        FROM NUM
    ) B 
WHERE B.IS_PRIME='PRIME' 
AND B.N!=1;

我知道这个问题已被多次询问,我要求更好的解决方案.更多关于如何使用MysqL / MS sql / Postgresql的输入.

任何帮助都会让我的理解变得更好.

解决方法:

在Postgresql中,打印素数高达1000的最快查询可能是：

SELECT regexp_split_to_table('2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,947,953,967,971,977,983,991,997',E',')::int
AS x
;

我的电脑只花了16毫秒.

>注意：从https://en.wikipedia.org/wiki/Prime_number复制了素数列表
并粘贴到这个长串

如果您更喜欢sql,那么这是有效的

WITH x AS (
  SELECT * FROM generate_series( 2, 1000 ) x
)
SELECT x.x
FROM x
WHERE NOT EXISTS (
  SELECT 1 FROM x y
  WHERE x.x > y.x AND x.x % y.x = 0
)
;

它慢了两倍–31毫秒.

Ans是Oracle的等效版本：

WITH x AS(
    SELECT level+1 x
    FROM dual
    CONNECT BY LEVEL <= 999
)
SELECT x.x
FROM x
WHERE NOT EXISTS (
  SELECT 1 FROM x y
  WHERE x.x > y.x AND remainder( x.x, y.x) = 0
)
;