in the absence of an index, it is true that using in in mysql is faster than using or, but I don"t understand why. Please give me some advice.
in the absence of an index, it is true that using in in mysql is faster than using or, but I don"t understand why. Please give me some advice.
it's like you go to the construction site to move bricks
< H2 > IN < / H2 >foreman IN said: if you go to construction site A today, 1000 will be enough.
< H2 > OR < / H2 >foreman OR said: I don't know where to move or how much I should move today. I'll tell you what, you go to construction site A, then to construction site B, and then to construction site N. go quickly and move more, the boss is happy.
who will be tired to death in the end.
SELECT * FROM tblName WHERE key IN(a1, a2, ..., an);if the index is not needed, traverse the key, of the whole table to match A1, a2,., an
therefore, the efficiency of IN is higher than that of OR,. With the increase of the range of parameter sets, the performance of IN will not decline too much, while the performance of OR will decline very much.
in the absence of an index, the efficiency of in will not decline much with the increase of the amount of data behind in or or, but the performance of or will deteriorate greatly as there are more records and more fields connected (1or2or3or4or.).
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