在 SQL 中,COUNT()
函數(shù)用于計(jì)算表中的行數(shù)或特定列中非空值的數(shù)量
SELECT COUNT(*) FROM table_name;
SELECT COUNT(column_name) FROM table_name;
WHERE
子句對(duì)結(jié)果進(jìn)行篩選:SELECT COUNT(*) FROM table_name WHERE condition;
GROUP BY
子句按特定列對(duì)結(jié)果進(jìn)行分組:SELECT column_name, COUNT(*) FROM table_name GROUP BY column_name;
這些示例展示了如何在 SQL 查詢中使用 COUNT()
函數(shù)來(lái)計(jì)算行數(shù)和非空值的數(shù)量。請(qǐng)根據(jù)實(shí)際需求調(diào)整查詢語(yǔ)句。