Syntax:
ALTER TABLE {TABLENAME}
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL}
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
WITH VALUES
Example:
ALTER TABLE SomeTable
ADD SomeCol Bit NULL --Or NOT NULL.
CONSTRAINT D_SomeTable_SomeCol --When Omitted a Default-Constraint Name is autogenerated.
DEFAULT (0)--Optional Default-Constraint.
WITH VALUES --Add if Column is Nullable and you want the Default Value for Existing Records.
Notes:
Optional Constraint Name:
If you leave out CONSTRAINT D_SomeTable_SomeCol
then SQL Server will autogenerate
a Default-Contraint with a funny Name like: DF__SomeTa__SomeC__4FB7FEF6
Optional With-Values Statement:
The WITH VALUES
is only needed when your Column is Nullable
and you want the Default Value used for Existing Records.
If your Column is NOT NULL
, then it will automatically use the Default Value
for all Existing Records, whether you specify WITH VALUES
or not.
How Inserts work with a Default-Constraint:
If you insert a Record into SomeTable
and do not Specify SomeCol
's value, then it will Default to 0
.
If you insert a Record and Specify SomeCol
's value as NULL
(and your column allows nulls),
then the Default-Constraint will not be used and NULL
will be inserted as the Value.
Notes were based on everyone's great feedback below.
Special Thanks to:
@Yatrix, @WalterStabosz, @YahooSerious, and @StackMan for their Comments.
You can use GROUP_CONCAT
:
SELECT person_id,
GROUP_CONCAT(hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Ludwig stated in his comment, you can add the DISTINCT
operator to avoid duplicates:
SELECT person_id,
GROUP_CONCAT(DISTINCT hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Jan stated in their comment, you can also sort the values before imploding it using ORDER BY
:
SELECT person_id,
GROUP_CONCAT(hobbies ORDER BY hobbies ASC SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Dag stated in his comment, there is a 1024 byte limit on the result. To solve this, run this query before your query:
SET group_concat_max_len = 2048;
Of course, you can change 2048
according to your needs. To calculate and assign the value:
SET group_concat_max_len = CAST(
(SELECT SUM(LENGTH(hobbies)) + COUNT(*) * LENGTH(', ')
FROM peoples_hobbies
GROUP BY person_id) AS UNSIGNED);
Best Answer
I always use the alias in the delete statement as it prevents the accidental
caused when failing to highlight the whole query before running it.