mysql 取各月的第一天

SELECT STR_TO_DATE(CONCAT(YEAR(date_column), '-', MONTH(date_column), '-01'), '%Y-%m-%d') AS first_day_of_month
FROM your_table;

SELECT DATE_ADD(DATE(date_column), INTERVAL -DAY(date_column) + 1 DAY) AS first_day_of_month
FROM your_table;

SELECT DATE_ADD(LAST_DAY(date_column), INTERVAL 1 DAY - INTERVAL DAY(LAST_DAY(date_column)) DAY) AS first_day_of_month
FROM your_table;

SELECT STR_TO_DATE(CONCAT(YEAR(date_column), '-', MONTH(date_column), '-01'), '%Y-%m-%d') AS first_day_of_month
FROM your_table;

CREATE INDEX idx_date_column ON your_table(date_column);

SELECT DATE_ADD(DATE(date_column), INTERVAL -DAY(date_column) + 1 DAY) AS first_day_of_month
FROM your_table
WHERE date_column >= '2023-01-01' AND date_column <= '2023-12-31';