MySQL - Selecting only the default value from column
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I am wondering is it possible to select only the default value of empty column? I have absolutely empty table and I want just to select one of the columns default value - it is important for my JAVA app which is filling the table.
You can get the default from the INFORMATION_SCHEMA.COLUMNS
select COLUMN_DEFAULT from INFORMATION_SCHEMA.COLUMNS where TABLE_SCHEMA='your_db' and TABLE_NAME='your_table' and COLUMN_NAME='your_column'
11.6 Data Type Default Values, An expression default value for one column can refer to other table columns, with SELECT , the destination table preserves expression default values from the to specify the default value for a named column is permitted only for columns� You can use a WHERE clause to combine row selection with column selection. For example, to get birth dates for dogs and cats only, use this query: For example, to get birth dates for dogs and cats only, use this query:
You can define a default value for a column when you create a table, if you just want MySQL to insert it automatically:
create table my_table (i INT DEFAULT 1);
But if you mean you want the default value which is stored in the DB dictionary, you can get it by this query:
SELECT Column_Default FROM Information_Schema.Columns WHERE Table_Schema = 'yourSchema' AND Table_Name = 'yourTableName' AND Column_Name = 'yourColumnName'
Changing a Column's Default Value, Changing a Column's Default Value Problem You want to leave a column definition alone except for the default value. Solution Use SET DEFAULT to specify the� The columns of the table output from VALUES have the implicitly named columns column_0, column_1, column_2, and so on, always beginning with 0. This fact can be used to order the rows by column using an optional ORDER BY clause in the same way that this clause works with a SELECT statement, as shown here:
I can only think of two ways:
Inserting a row
- Insert a row without specifying a value for that column
- Select the column from that row; it will have the default value of the column
- Delete the row
...probably all in a transaction so nothing else sees it.
describe command (aka
explain) describes objects in the system, including tables. So if you do
explain YourTable, you'll get back information about the table, including its default values.
Here's an example from that linked documentation:
mysql> DESCRIBE City; +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+ | Field | Type | Null | Key | Default | Extra | +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+ | Id | int(11) | NO | PRI | NULL | auto_increment | | Name | char(35) | NO | | | | | Country | char(3) | NO | UNI | | | | District | char(20) | YES | MUL | | | | Population | int(11) | NO | | 0 | | +−−−−−−−−−−−−+−−−−−−−−−−+−−−−−−+−−−−−+−−−−−−−−−+−−−−−−−−−−−−−−−−+
So you can extract the default from the
Default column in the returned rows.
Ah, of course, there's a third way, see slaakso's answer for it.
MySQL: Select a default value for NULL fields, MySQL: Select a default value for NULL fields and can not use Ruby objects you may run into problems when encountering fields with NULL values: Mysql:: Error: BLOB/TEXT column can't have a default value There could be multiple values for those columns per group but only one value can be picked for the results. In this case, the column’s default value reverts to the standard default for the column type. For columns that can contain NULL values, this will be NULL . Otherwise, the general defaults are 0, the empty string, or the “zero” date or time for numeric, string, or date or time columns, respectively.
SQL DEFAULT Constraint, The DEFAULT constraint is used to provide a default value for a column. MySQL: ALTER TABLE Persons ALTER City DROP DEFAULT;. SQL Server / Oracle� With one exception, the default value specified in a DEFAULT clause must be a literal constant; it cannot be a function or an expression. This means, for example, that you cannot set the default for a date column to be the value of a function such as NOW() or CURRENT_DATE.
CREATE TABLE, NULL and NOT NULL; DEFAULT Column Option; AUTO_INCREMENT SELECT , because it allows to create a table into a database, which contains The default value will be used if you INSERT a row without specifying a value for COLUMN_FORMAT is only used by MySQL Cluster, and is silently ignored in MariaDB. Select Rows with Maximum Value on a Column Example 2. In this example, we will show how to select rows with max value along with remaining columns. It is useful if you want to return the remaining columns (non-group by columns). For this SQL Server example, we used the Inner Join to join the employee table with itself.
Insert row with only default values in MySQL, Insert row with only default values in MySQL at the time of table creation and it will insert default value whenever you do not provide the value for that column. Display all records from the table using select statement − The collation for nonbinary string columns, or NULL for other columns. This value is displayed only if you use the FULL keyword. Null. The column nullability. The value is YES if NULL values can be stored in the column, NO if not. Key. Whether the column is indexed:
- Ah, I tend to forget about
INFORMATION_SCHEMAfor some reason, that's the third (or perhaps first) way. :-)
- Codd's 4th rule ;)