If a Cloud Spanner table is created with nullable columns, is it possible to add a NOT NULL constraint on a column without recreating the table?
You can add a NOT NULL constraint to a non-key column. You must first ensure that all rows actually do have values for the column. Spanner will scan the data to verify before fully applying the NOT NULL constraint. More information about how to alter tables is here and here.
However, you can not add such a constraint to a key column. That kind of change would require rewriting all the data in the table, because the nullness of the key affects how the data is encoded. The only option for making that change is to create a new table that's set up the way you want, make code changes to support using both tables temporarily, gradually move the data from the old table to the new table, and eventually change the code to use only the new table and drop the old table. If you further then wanted the original table name, you'd have to do the whole thing again.
Unfortenately there is not way to add not null column
The way to do it:
1 add nullable column
ALTER TABLE table1 ADD COLUMN column1 STRING(255)
UPDATE table1.column1, SET NOT NULL VALUE to the column (if the table is not empty).
UPDATE TABLE table1 SET column1 = "<GENERATED DATA>"
Add constraint
ALTER TABLE table1 ADD COLUMN column1 STRING(255) NOT NULL
Thanks.
Creating a non-nullable column in Spanner on an existing table is typically a three step process:
# add new column to table
ALTER TABLE <table_name> ADD COLUMN <column_name> <value_type>;
# create default values
UPDATE <table_name> SET <column_name>=<default_value> WHERE TRUE;
# add constraint
ALTER TABLE <table_name> ALTER COLUMN <column_name> <value_type> NOT NULL;
Related
I want to display image in report column. My table has composite primary key: ID and DATE.
When I add these columns in BLOB attributes as Primary Key Column 1 and Primary Key Column 2 report can not find data because of DATE column. Is it a problem in date format, or something else?
I'd suggest you to use only one column as a primary key column (a sequence or - if your database version supports it - an identity column).
Combination of [ID, DATE] you currently have can then be set to unique key (set both columns NOT NULL to "mimic" what primary key would do).
Why? Although your data model probably is just fine, certain Apex functionalities "suffer" from such things and prefer having a single-column primary keys.
I have a large target table with columns (id, value). I want to update value='old' to value='new'.
The simplest way would be to UPDATE target SET value='new' WHERE value='old';
However, this deletes and creates new rows and is not recommended, possibly. So I tried to do a merge column update:
# staging
CREATE TABLE stage (LIKE target INCLUDING DEFAULTS);
INSERT INTO stage (SELECT id, value FROM target WHERE value=`old`);
UPDATE stage SET value='new' WHERE value='old'; # ??? how do you update value?
# merge
begin transaction;
UPDATE target
SET value = stage.value FROM stage
WHERE target.id = stage.id and target.distkey = stage.distkey; # collocated join?
end transaction;
DROP TABLE stage;
This can't be the best way of creating the table stage: I have to do all these UPDATE delete/writes when I update this way. Is there a way to do it in the INSERT?
Is it necessary to force the collocated join when I use CREATE TABLE LIKE?
Are you updating all the rows in the table?
If yes you can use CTAS (create table as) which is recommended method
Assuming you table looks like this
table1
id, col1,col2, value
You can use the following SQL to create a new table
CREATE TABLE tmp_table AS
SELECT id, col1,col2, 'new_value'
FROM table1;
After you verify data in tmp_table
DROP TABLE table1;
ALTER TABLE tmp_table RENAME TO table1;
If you are not updating all the rows you can use a filter to do a CTAS and insert the rest of the rows to the new table, let me know if you need more info if this is the case
CREATE TABLE tmp_table AS
SELECT id, col1,col2, 'new_value'
FROM table1
WHERE value = 'old'
INSERT INTO tmp_table SELECT * from table1;
Next step would be DROP the tmp table and rename table1
Update: Based on your comment you can do the following, let me know if this solves your case.
This method basically creates a new table to replace your existing table.
I have used some of your code
CREATE TABLE stage (LIKE target INCLUDING DEFAULTS);
INSERT INTO stage SELECT id, 'new' FROM target WHERE value=`old`;
Above INSERT inserts rows to be updated with 'new', no need to run an UPDATE after this.
Bring unchanged rows
INSERT INTO stage SELECT id, value FROM target WHERE value!=`old`;
After this point you have target table which is your original table intact
stage table will have both sets of rows, updated rows with 'new' value and rows you did not want to change
To replace your target with stage
DROP TABLE target;
or to keep it further verification
ALTER TABLE target RENAME TO target_old;
ALTER TABLE stage RENAME TO target;
From a redshift developer:
This case doesn't require an upsert, or update+insert, and it is fine to just run the update:
UPDATE target SET value='new' WHERE value='old';
Another way would be to INSERT the rows you need and DELETE the other rows, but that's unnecessarily complicated.
In my model I have table AssignedToUser that don't contain any NULL values.
Table TotalCounts contains number of tasks for each User.
Those two table joined on UserGUID, and table TotalCounts contains NULL value for UserGUID.
When I drop everything in one table there is NULL value for AssignedToUser.
How can I substitute value NULL for AssignedToUser for "POOL".
Under EditQuery I tried to Create additional column
if [AssignedToUser] = null then "POOL" else [AssignedToUser]
But that didnt help.
UPDATE:
Thanks Alexis.
I have created FullAssignedToUsers table, but when I try to make a relationship with TotalCounts on UserGUID - it doesnt like it.
Data in new a table looks like this:
UPDATE:
File .ipbx can be accessed here:
https://www.dropbox.com/s/95frggpaq6tce7q/User%20Open%20Closed%20Tasks%20Experiment.pbix?dl=0
I believe the problem here is that your join has UserGUID values that are not in your AssignedToUsers table.
To correct this, one possibility is to replace your AssignedToUsers table with one that contains all the UserGUID values from the TotalCounts table.
FullAssignedToUsers =
ADDCOLUMNS(VALUES(TotalCounts[UserGUID]),
"AssignedToUser",
LOOKUPVALUE(AssignedToUsers[AssignedToUser],
AssignedToUsers[UserGUID], TotalCounts[UserGUID]))
The should get you the full outer join. You can then create the custom column like you described in the table and use that column in your visual.
You'll probably want to break the relationships with the original AssignedToUsers table and create relationships with the new one instead.
If you don't want to take that extra step, you can do an ISBLANK inside your new table formula.
FullAssignedToUsers =
ADDCOLUMNS(VALUES(TotalCounts[UserGUID]),
"AssignedToUser",
IF(
ISBLANK(
LOOKUPVALUE(AssignedToUsers[AssignedToUser],
AssignedToUsers[UserGUID], TotalCounts[UserGUID])),
"POOL",
LOOKUPVALUE(AssignedToUsers[AssignedToUser],
AssignedToUsers[UserGUID], TotalCounts[UserGUID])))
Note: This is equivalent to doing a right outer join merge on the AssignedToUsers table in the query editor and then replacing the nulls with "POOL". I'd actually recommend approaching it that way instead.
Another way to approach it is to pull the AssignedToUser column over to the TotalCounts table in a custom column and use that column in your visual instead.
AssignedToUsers =
IF(ISBLANK(RELATED(AssignedToUsers[AssignedToUser])),
"POOL",
RELATED(AssignedToUsers[AssignedToUser]))
This is equivalent to doing a left outer join merge on the TotalCounts table in the query editor, expanding the AssignedToUser column, then replacing nulls with "POOL" in that column.
In Dax missing values are Blank() not null. Try this:
=IF(
ISBLANK(AssignedToUsers[AssignedToUser]),
"Pool",
AssignedToUsers[AssignedToUser]
)
I have a source table named A in oracle.
Initially Table A is loaded(copied) into table B
next I operate DML on Table A like Insert , Delete , Update .
How do we reflect it in table B ?
without creating any extra column in target table.
Time stamp for the row is not available.
I have to compare the rows in source and target
eg : if a row is deleted in source then it should be deleted in target.
if a row is updated then update in target and if not available in source then insert it in the target .
Please help !!
Take A and B as source.
Do a full outer join using a joiner (or if both tables are in the same databse, you can join in Source Qualifier)
In a expression create a flag based on the following scenarios.
A key fields are null => flag='Delete',
B key fields are null => flag='Insert',
Both A and B key fields are present - Compare non-key fields of A and B, if any of the fields are not equal set flag to 'Update' else 'No Change'
Now you can send the records to target(B) after applying the appropriate function using Update Strategy
If you do not want to retain the operations done in target table (as no extra column is allowed), the fastest way would simply be -
1) Truncate B
2) Insert A into B
I create a program to sync tables between 2 databases.
I use this common code:
DbSyncScopeDescription myScope = new DbSyncScopeDescription("myscope");
DbSyncTableDescription tblDesc = SqlSyncDescriptionBuilder.GetDescriptionForTable("Table", onPremiseConn);
myScope.Tables.Add(tblDesc);
My program creates the tracking table only with Primary Key (id column).
The sync is ok to delete and insert rows.
But updating don't. I need update all the columns and they are not updated (For example: a telephone column).
I read that I need to add the columns I want to sync MANUALLY with this code:
Collection<string> includeColumns = new Collection<string>();
includeColumns.Add("telephone");
...
includeColumns.Add(Last column);
And changing the table descripcion in this way:
DbSyncTableDescription tblDesc = SqlSyncDescriptionBuilder.GetDescriptionForTable("Table", includeColumns, onPremiseConn);
Is there a way to add all the columns of the table automatically?
Something like:
Collection<string> includeColumns = GetAllColums("Table");
Thanks,
SqlSyncDescriptionBuilder.GetDescriptionForTable("Table", onPremiseConn) will include all the columns of the table already.
the tracking tables only stores the PK and filter columns and some Sync Fx specific columns.
the tracking is at row level, not column level.
during sync, the tracking table and its base table are joined to get the row to be synched.