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14 sie 2009 · mysql> create table foo (str1 varchar (300), str2 varchar (300)); mysql> alter table foo modify str2 varchar (65353); ERROR 1118 (42000): Row size too large. The maximum row size for the used table type, not counting BLOBs, is 65535. You have to change some columns to TEXT or BLOBs.
10 cze 2011 · There is no simple answer; it depends on the data type of the column, whether the column is indexed; and the storage engine. The impact of using NULL for a column can vary from nothing to several bytes (depending on how many other columns are also NULL-able.)
In MySQL, 0 or NULL means false and anything else means true. The default truth value from a boolean operation is 1. NULL instead of death <>. NULL. Two NULL values are regarded as equal in a GROUP BY. When doing an ORDER BY, NULL values are presented first if you do ORDER BY ... ASC and last if you do ORDER BY ...
For MyISAM tables, NULL columns require additional space in the row to record whether their values are NULL. Each NULL column takes one bit extra, rounded up to the nearest byte.
31 lip 2024 · When creating tables in MySQL we can specify whether a column allows the NULL values or not. By default, columns can contain NULL values unless specified otherwise. In MySQL, NULL represents a missing, unknown, or undefined value. It is not equivalent to the empty string (”) or zero (0).
8 wrz 2015 · Step 1: SELECT COUNT(*)-- use this in place of Rows. Step 2: Get Data_length + Index_length + Data_free. Step 3: Divide.
The IS NULL operator is used to test for empty values (NULL values). The following SQL lists all customers with a NULL value in the "Address" field: Example Get your own SQL Server. SELECT CustomerName, ContactName, Address. FROM Customers. WHERE Address IS NULL; Try it Yourself » Tip: Always use IS NULL to look for NULL values.
