Lets suppose I have two schemas in one DB: public and private. In both schemas I have the same table - my_table with the same columns. So is it normal to do the following:
SELECT public.my_table.my_col FROM public.my_table?
I am trying to do it with H2 but get exception in ResultSet - column not found. Is it not normal or it's not normal for H2?
You should write:
SELECT my_col FROM public.my_table
since column names are already evaluated in the table(s) specified in the query.
Related
I have a look-up table containing a list of fully qualified table paths in a Big Query table called all_tables. For example
|table_list|
|----------|
|project_name.dataset_name1.table_1|
|project_name.dataset_name2.table_1|
|project_name.dataset_name3.table_1|
|project_name.dataset_name4.table_1|
|project_name.dataset_name5.table_1|
I am trying to iterate through these tables to pull out elements I need for another procedure using the for-in syntax in Big Query. This is a simplified version of the query I am using
```
FOR table IN (select * from my_project.my_dataset.all_tables)
DO
select * from table;
END FOR;
```
This isn't working. It picks up the list of tables correctly, but when it substitutes the dataset name in the line 3 select statement, it says
**Invalid value: Table "table" must be qualified with a dataset (e.g. dataset.table)**
I know what the error is, but I am not sure how to make it 'see' the value of table as a table path.
All paths are correct, and I am doing it this way as I am querying multiple tables across multiple datasets for a table creation query.
You should a dynamic sql to refer the table name as a variable, so consider below query:
FOR table IN (select * from my_project.my_dataset.all_tables)
DO
EXECUTE IMMEDIATE FORMAT("""
SELECT * FROM %s;
""", table.table_list);
END FOR;
What is the purpose of the two dots in the following SQL statement?
select * from msdb..backupset
I understand that one would mean select from the table called 'backupset' with the 'msdb' database. But two dots is doing something different, which I do not understand.
The login would have default "schema" on the database that is connected to (in your case msdb). Specifying the object (in your case "backupset") with 3-part name like [DB name]..[Object Name] is omitting of the schema name (in your case probably "dbo") in the 3-part name.
There could be MyDatabase.SchemaA, and MyDatabase.SchemaB on a database MyDatabase database, and each schema could have 2 separate tables with same object name -- like MyDatabase.SchemaA.MyTable, and MyDatabase.SchemaB.MyTable.
If your login to MyDatabase defaults to SchemaA, and and run SELECT * FROM MyDatabase..MyTable, then you would be selecting from MyDatabase.SchemaA.MyTable.
If you wanted to select from the second table, you'd have to SELECT * FROM MyDatabase.SchemaB.MyTable or SELECT * FROM SchemaB.MyTable
Typically it is said that specifying the schema name explicitly is good practice (instead of backupset or MyTable, write dbo.backupset or SchemaA.MyTable
Using the two dots in this three-part naming convention (i.e Database.schema.table) indicates that the schema is the default schema(dbo)
I have a column name "CustomerIDClass" and I need to find the table it's associated with within an entire Oracle database.
I've run this to determine the owner and name of the table where this column name appears:
select * from DBA_TAB_COLUMNS
where COLUMN_NAME LIKE '%CustomerIDClass%';
and I'm getting this response:
I don't have enough reputation to post the image, so here's the link: http://i.imgur.com/a7rcKoA.png
I have no idea how to access this (BIN$Csew==) table. When I try to use it as a table name I get errors or messages saying that no rows were returned.
My main goal here is to write a simple statement that lets me search the database for the "CustomerIDClass" and view the table that contains this column name.
This table is in the recycle bin. You have to issue FLASHBACK TABLE "Customer1"."BIN$Csew==$0" TO BEFORE DROP command, given you have the appropriate privileges.
Doc: http://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_9012.htm
Do note that in oracle the column names are stored in capital but you are using mixed case in your like statement therefore the select clause will not return any result
Try the below
select * from DBA_TAB_COLUMNS
where COLUMN_NAME LIKE '%CUSTOMERIDCLASS%';
HyperSQL supports different table types (memory, cached etc.).
How can I get the type of an existing table?
SELECT HSQLDB_TYPE
FROM INFORMATION_SCHEMA.SYSTEM_TABLES
WHERE TABLE_NAME = '<TABLE NAME IN UPPERCASE>'
HSQL converts table names to uppercase so the table name in the query also have to be in uppercase.
How can I add a column in an SQLite table if and only if the same column does not exist in the table?
Using ALTER TABLE I am able to create a new column but want to know how to check whether that column already exists in the table or not?
SQLite returns an error like "no such column: foo" if the table doesn't contain the column:
select foo from yourTable limit 1
Also you can get the create-table statement:
select sql from sqlite_master where tbl_name = 'YourTableName'
and then parse the result, looking for the column-name. I don't know of an elegant way to query the list of columns for a specified table, though one may exist.
Also if you attempt to do this:
alter table YourTable add column foo {column-def whatever it is}
you get an error from SQLite if the column already exists. You could trap that error too.
Finally you could do this:
select sql from sqlite_master
where tbl_name = 'YOURTABLE' and sql like '%"foo" CHAR%'; -- or whatever type
and if the specified table contains the column which is surrounded by double-quotes in the query, and with the type you have specified, you will get a result, otherwise an empty set. Specifying the datatype ensures that your LIKE substring match occurs on a column-name.
There's no way (that I know of) to do it all in a single SQLite query. You must use application code to manage the If/Elseness.
Check if table exists or not:
select count(*) from sqlite_master where type = 'table' and name = MyTable';
Check if column exists in table or now
pragma table_info(thumbnail);
However, a better approach may be explicit database schema updates based on schema versions your application maintains (e.g. specific alter table statement to go from schema version 1 to 2):
pragma user_version;
It seems like that it is impossible to do checking if the column not exists and addindg the new column in one command, because Sqlite don't support "IF NOT EXISTS" for column. "IF NOT EXISTS" works only on table.
Here is what I will do:
rev = ExecuteStatement("SELECT columnNamexx FROM tableNamexx limit 1;");
if(rev != SQLITE_OK){ // add col to table
ExecuteStatement("ALTER TABLE tableNamexx ADD COLUMN columnNamexx INTEGER DEFAULT 0;");
}
You can view the table columns by using '.schema tableName'