官方文档有cursor.rowcount ，但通常返回值是-1。
查询相关资料，得到答案如下：
没有可以直接得到行数的函数。sqlite事先不知道行数，遍历时才逐行返回。—>遍历完才知道的话，是否意味着并没有一次过将全部数据返回写入内存？
可以用 : result=cursor.fetchall() 然后 count=len(result) 获取。
或者执行一次 select count(*) from x where y 然后 fetchone 获取
Q) Which func could get the number of rows?
A) There is no function to retrieve the number of rows in a result set. SQLite doesn’t know the number in advance, but returns row by row while iterating through the tables. The application can increment a row counter as needed at every successful sqlite3_step() .
Some wrappers are able to collect all rows in a resultset in a in-memory table, so they can return the number of rows.
You can always get the number of rows that a certain SELECT statement would return at the cost of some performance:
BEGIN IMMEDIATE TRANSACTION;
SELECT COUNT(*) FROM x WHERE y;
SELECT a,b,c FROM x WHERE y;
ROLLBACK TRANSACTION;
You have to wrap this in a transaction to prevent other connections from inserting / deleting rows between the two SELECT statements.
rowcount返回的仅仅是受影响的行，select不会影响这些行。 所有的 SELECT语句都不会有 rowcount
Original: https://blog.csdn.net/bigcarp/article/details/114193423
Author: bigcarp
Title: python sqlite3 如何得到select 语句返回的记录集的行数？
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