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String Functions: ASCII CHAR_LENGTH CHARACTER_LENGTH CONCAT CONCAT_WS FIELD FIND_IN_SET FORMAT INSERT INSTR LCASE LEFT LENGTH LOCATE LOWER LPAD LTRIM MID POSITION REPEAT REPLACE REVERSE RIGHT RPAD RTRIM SPACE STRCMP SUBSTR SUBSTRING SUBSTRING_INDEX TRIM UCASE UPPER Numeric Functions: ABS ACOS ASIN ATAN ATAN2 AVG CEIL CEILING COS COT COUNT DEGREES DIV EXP FLOOR GREATEST LEAST LN LOG LOG10 LOG2 MAX MIN MOD PI POW POWER RADIANS RAND ROUND SIGN SIN SQRT SUM TAN TRUNCATE Date Functions: ADDDATE ADDTIME CURDATE CURRENT_DATE CURRENT_TIME CURRENT_TIMESTAMP CURTIME DATE DATEDIFF DATE_ADD DATE_FORMAT DATE_SUB DAY DAYNAME DAYOFMONTH DAYOFWEEK DAYOFYEAR EXTRACT FROM_DAYS HOUR LAST_DAY LOCALTIME LOCALTIMESTAMP MAKEDATE MAKETIME MICROSECOND MINUTE MONTH MONTHNAME NOW PERIOD_ADD PERIOD_DIFF QUARTER SECOND SEC_TO_TIME STR_TO_DATE SUBDATE SUBTIME SYSDATE TIME TIME_FORMAT TIME_TO_SEC TIMEDIFF TIMESTAMP TO_DAYS WEEK WEEKDAY WEEKOFYEAR YEAR YEARWEEK Advanced Functions: BIN BINARY CASE CAST COALESCE CONNECTION_ID CONV CONVERT CURRENT_USER DATABASE IF IFNULL ISNULL LAST_INSERT_ID NULLIF SESSION_USER SYSTEM_USER USER VERSION
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SQL Working With Dates

SQL Dates

The most difficult part when working with dates in databases, is to be sure that the format of the date you are trying to insert/select, matches the format of the date column in the database.

SQL Date Data Types

Different SQL databases have various data types to store date and time values.

MySQL has the following date data types:

  • DATE - format YYYY-MM-DD
  • DATETIME - format: YYYY-MM-DD HH:MI:SS
  • TIMESTAMP - format: YYYY-MM-DD HH:MI:SS
  • TIME - format: HH:MI:SS
  • YEAR - format YYYY or YY

SQL Server has the following date data types:

  • DATE - format YYYY-MM-DD
  • DATETIME - format: YYYY-MM-DD HH:MI:SS
  • SMALLDATETIME - format: YYYY-MM-DD HH:MI:SS
  • TIME - format: HH:MI:SS
  • TIMESTAMP - format: a unique number

Note: The date data type are defined for a column upon creation of a new table in your database.

SQL Working with Dates

Look at the following table:

Orders Table

OrderId ProductName OrderDate
1 Geitost 2025年11月11日
2 Camembert Pierrot 2025年11月09日
3 Mozzarella di Giovanni 2025年11月11日
4 Mascarpone Fabioli 2025年10月29日

Now we want to select the records with an OrderDate of "2025年11月11日" from the table above.

We use the following SELECT statement:

SELECT * FROM Orders WHERE OrderDate='2025-11-11'

The result-set will look like this:

OrderId ProductName OrderDate
1 Geitost 2025年11月11日
3 Mozzarella di Giovanni 2025年11月11日

Note: Two dates can easily be compared if there is no time component involved!

Now, assume that the "Orders" table looks like this (notice the added time-component in the "OrderDate" column):

OrderId ProductName OrderDate
1 Geitost 2025年11月11日 13:23:44
2 Camembert Pierrot 2025年11月09日 15:45:21
3 Mozzarella di Giovanni 2025年11月11日 11:12:01
4 Mascarpone Fabioli 2025年10月29日 14:56:59

If we use the same SELECT statement as above:

SELECT * FROM Orders WHERE OrderDate='2025-11-11'

we will get no result! This is because the query is looking only for dates with no time portion.

Tip: To keep your queries simple and easy to maintain, do not use time-components in your dates, unless you have to!


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