From the documentation I can figure out how to replace or add a value at from an existing property
{"example":123}
UPDATE mytable
SET jsoncolumn = jsonb_set(jsoncolumn, '{example}', '"string123"')
WHERE id = 1;
{"example":"string123"}
However, I cannot figure out how to insert a property at the top level (beside a sibling)
{"example":123}
{"example":123,"property-to-add":"value"}
What is the easiest way to accomplish this (given that the actual object is pretty large)
You can append the new key/value pair:
UPDATE mytable
SET jsoncolumn = jsoncolumn || '{"property-to-add": "value"}'
WHERE id = 1;
If property-to-add already exists, it will be replaced.
Related
I have a table af with columns af.id, etc. and a table af_pb with columns af_id and pb_id (which assigns entities from table pb to the entities of table af).
What i want:
add a new column precedence in table af
for each af.id in af:
if there is a pair (af_id, pb_id) with af.id = af_id and some pb_id in the join table af_pb, then set af.precedence = 0
if there is no such pair, set af.precedence = 1
How can i reach this in PostgreSQL? I already read about the case-when-else-statement but I didn't managed to implement it such that the column precedence is set correctly.
While this can be done in with a case expression, it is not necessary. If you want a default value for later inserts into table af then alter the table with it, then update to set the non-default.
alter table af add column precedence integer default 1;
update af
set precedence = 0
where exists (select null
from af_pb
where af.af_id = af_pb.af_id);
If a default is not desired then a just add the column and afterward update to set the appropriate value:
alter table af add column precedence integer;
update af
set precedence =
( not (exists (select null
from af_pb
where af.af_id = af_pb.af_id)))::integer;
I'm sure this could be a duplicate but I can't seem to find the right search phrase.
Given a table in a named schema (i.e. not dbo) requires you include the schema name in the statement. So previously I'd have simply written it as so:
UPDATE [Schema].[Table1]
SET [AColumn] =
(
SELECT [SomeColumn]
FROM [Schema].[Table2]
WHERE [Schema].[Table2].[SameColumnName] = [Schema].[Table1].[SameColumnName]
);
But since More than two-part column name is deprecated, I need to find a new way to do this which is future proof. I have come up with 2 options, firstly using an alias:
UPDATE [Alias1]
SET [AColumn] =
(
SELECT [SomeColumn]
FROM [Schema].[Table2] [Alias2]
WHERE [Alias2].[SameColumnName] = [Alias1].[SameColumnName]
)
FROM [Schema].[Table1] [Alias1];
The second way is the one I'm really having trouble finding out if it's truly VALID T-Sql:
UPDATE [Schema].[Table1]
SET [AColumn] =
(
SELECT [SomeColumn]
FROM [Schema].[Table2]
WHERE [Table2].[SameColumnName] = [Table1].[SameColumnName]
);
I have tested both and they work, so my question is, is the second completely valid and normal to use just the table name without the Schema in this sense or should I rather opt for the slightly more verbose Alias?
As I said in my comment, alias your objects.
SELECT MT.MyColumn,
YT.MyColumn
FROM dbo.MyTable MT
JOIN so.YourTable YT ON MT.ID = YT.fID
WHERE YT.[name] = N'Jane';
If you're performing an UPDATE, then specify the alias of the object to Update:
UPDATE MT
SET MyColumn = YT.MyColumn --Column on the left side of the SET will always reference the table being updated
FROM dbo.MyTable MT
JOIN so.YourTable YT ON MT.ID = YT.fID
WHERE YT.[name] = N'Jane';
I need to split the same record two time.
For example, if I have in MyTable five record I need to show in Form's Grid ten record.
If It's possible I can create a View, I just to duplicate one time the same record.
This is my start point :
I want to duplicate the record :
In MyForm can't edit anything, is only View. No Delete, No Edit, No Create
Thanks in advance!
This sounds like an exercise, which we probably shouldn't be giving you the answer to...but try creating MyTableJoin and create a foreign key relation to MyTable.Id then add a field called MyTableJoin.Row and populate the table with 2 matching rows for every 1 row in MyTable. Then on your form, join MyTableJoin.
So:
MyTableJoin.clear();
MyTableJoin.Id = "ID_I";
MyTableJoin.Row = 1;
MyTableJoin.insert();
MyTableJoin.clear();
MyTableJoin.Id = "ID_I";
MyTableJoin.Row = 2;
MyTableJoin.insert();
MyTableJoin.clear();
MyTableJoin.Id = "ID_II";
MyTableJoin.Row = 1;
MyTableJoin.insert();
MyTableJoin.clear();
MyTableJoin.Id = "ID_II";
MyTableJoin.Row = 2;
MyTableJoin.insert();
You can create a union view and add same table twice. Just be shore to select union all option so that you do not get unique results.
I'm writing some triggers to check if an arrtibute of a newly create tuple is present in another table. What is the best way to check this?
IF (SELECT * FROM TABLEB where NEW.Attribute = Attribute) = NULL THEN
return NULL
END IF
Is there a better way? And does a Select that returns nothing = NULL or empty set?
Use IF EXISTS (SELECT * FROM TABLEB where NEW.Attribute = Attribute).
An empty rowset isn't the same as NULL, which represents an empty cell of a row. Your syntax would only be valid if the query only selected one row, in which case PostgreSQL will allow use of comparison operators against the top cell returned, which counts as NULL if none are returned.
How to set an object to null.
Ex:
my object samp contains three fileds
samp.field1,samp.field2.sampfield3
If i set samp:= null;
im getting errors is there a way to set the object value to null.
An sql database does not know about objects, it deals with rows in table.
To remove a row use DELETE :
e.g. :
DELETE FROM samp WHERE id = 12345;
DELETE FROM samp WHERE field1 = 'Delete Me';
The first example is typical to remove individual rows uing their primary key (id in this case)
The second example will remove a group of rows which have a speciic value for a field.