I need to insert into a simple table with two columns.
The first column has to contain the same value from row to row, while the second has to hold the various values from a source table. So it all should look like this:
Question is - is there a way to make a set-based insert in this case? The way I do it now is simply iterate through the rows of the source table. Or it's also possible to use cursors, only I'm not sure which is best.
But still this is iteration.
Any means to get around this?
Thanks in advance!
If you know your static value ahead of time, you could do something like this:
INSERT INTO targetTable(Col1, Col2)
SELECT 1, yourColumn
FROM sourceTable
WHERE <condition>
This is assuming that 1 is your static value. It can be replaced with the real value, or a variable, depending on the specifics of your query.
insert into dest_tab(col1, col2)
select 1, col2
from src_table
where ....
Related
In a statement like this:
update tab1 set (col1,col2)=(val1,val2) returning "?"
I send whole row for update on new values, RETURNING * gives back the whole row, but is there a way to check which exactly column has changed when others remained the same?
I understand that UPDATE rewrites the values, but maybe there is some built-in function for such comparison?
Basically, you need the pre-UPDATE values of updated rows to compare. That's kind of hard as RETURNING only returns post-UPDATE state. But can be worked around. See:
Return pre-UPDATE column values using SQL only
So this does the basic trick:
WITH input(col1, col2) AS (
SELECT 1, text 'post_up' -- "whole row"
)
, pre_upd AS (
UPDATE tab1 x
SET (col1, col2) = (i.col1, i.col2)
FROM input i
JOIN tab1 y USING (col1)
WHERE x.col1 = y.col1
RETURNING y.*
)
TABLE pre_upd
UNION ALL
TABLE input;
db<>fiddle here
This is assuming that col1 in your example is the PRIMARY KEY. We need some way to identify rows unambiguously.
Note that this is not safe against race conditions between concurrent writes. You need to do more to be safe. See related answer above.
The explicit cast to text I added in the CTE above is redundant as text is the default type for string literals anyway. (Like integer is the default for simple numeric literals.) For other data types, explicit casting may be necessary. See:
Casting NULL type when updating multiple rows
Also be aware that all updates write a new row version, even if nothing changes at all. Typically, you'd want to suppress such costly empty updates with appropriate WHERE clauses. See:
How do I (or can I) SELECT DISTINCT on multiple columns?
While "passing whole rows", you'll have to check on all columns that might change, to achieve that.
I feel like this should be simple but I'm relatively unskilled in SQL and I can't seem to figure it out. I'm used to wrangling data in python (pandas) or Spark (usually pyspark) and this would be a one-liner in either of those. Specifically, I'm using Snowflake SQL, but I think this is probably relevant to a lot of flavors of SQL.
Essentially I just want to trim the first character off of a specific column. More generally, what I'm trying to do is replace a column with a substring of the same column. I would even settle for creating a new column that's a substring of an existing column. I can't figure out how to do any of these things.
On obvious solution would be to create a temporary table with something like
CREATE TEMPORARY TABLE tmp_sub AS
SELECT id_col, substr(id_col, 2, 10) AS id_col_sub FROM table1
and then join it back and write a new table
CREATE TABLE table2 AS
SELECT
b.id_col_sub as id_col,
a.some_col1, a.some_col2, ...
FROM table1 a
JOIN tmp_sub b
ON a.id_col = b.id_col
My tables have roughly a billion rows though and this feels extremely inefficient. Maybe I'm wrong? Maybe this is just the right way to do it? I guess I could replace the CREATE TABLE table2 AS... to INSERT OVERWRITE INTO table1 ... and at least that wouldn't store an extra copy of the whole thing.
Any thoughts and ideas are most welcome. I come at this humbly from the perspective of someone who is baffled by a language that so many people seem to have mastery over.
I'm not sure the exact syntax/functions in Snowflake but generally speaking there's a few different ways of achieving this.
I guess the general approach that would work universally is using the SUBSTRING function that's available in any database.
Assuming you have a table called Table1 with the following data:
+-------+-----------------------------------------+
Code | Desc
+-------+-----------------------------------------+
0001 | 1First Character Will be Removed
0002 | xCharacter to be Removed
+-------+-----------------------------------------+
The SQL code to remove the first character would be:
select SUBSTRING(Desc,2,len(desc)) from Table1
Please note that the "SUBSTRING" function may vary according to different databases. In Oracle for example the function is "SUBSTR". You just need to find the Snowflake correspondent.
Another approach that would work at least in SQLServer and MySQL would be using the "RIGHT" function
select RIGHT(Desc,len(Desc) - 1) from Table1
Based on your question I assume you actually want to update the actual data within the table. In that case you can use the same function above in an update statement.
update Table1 set Desc = SUBSTRING(Desc,2,len(desc))
You didn't try this?
UPDATE tableX
SET columnY = substr(columnY, 2, 10 ) ;
-Paul-
There is no need to specify the length, as is evidenced from the following simple test harness:
SELECT $1
,SUBSTR($1, 2)
,RIGHT($1, -2)
FROM VALUES
('abcde')
,('bcd')
,('cdef')
,('defghi')
,('e')
,('fg')
,('')
;
Both expressions here - SUBSTR(<col>, 2) and RIGHT(<col>, -2) - effectively remove the first character of the <col> column value.
As for the strategy of using UPDATE versus INSERT OVERWRITE, I do not believe that there will be any difference in performance or outcome, so I might opt for the UPDATE since it is simpler. So, in conclusion, I would use:
UPDATE tableX
SET columnY = SUBSTR(columnY, 2)
;
I intend to write a INSERT INTO request in Postgresql based on several SELECT but didn't succeed.
I have one table containing data I select (srctab), and another one where I insert data (dsttab).
Here is what I run :
INSERT INTO dsttab (dstfld1, dstfld2) WITH
t1 AS (
SELECT srcfld1
FROM srctab
WHERE srcfld3 ='foo'
),
t2 AS (
SELECT srcfld5
FROM srctab
WHERE srcfld6 ='bar'
) select srcfld1, srcfld5 from srctab;
Could you please help to make this work ? Thank you !
Note: I'm guessing about what you want to do here. My guess is that you want to insert a single row with the values from the CTEs (That's the WITH block.). Your query as written would insert a row into dsttab for every row in srctab, if it were valid syntax.
You don't really need a CTE here. CTEs should really only be used when you need to reference the same subquery more than once; that's what they exist for. (Occasionally, you can somewhat abuse them to control certain performance aspects in PostgreSQL, but that isn't the case in other DBs and is something to be avoided when possible anyway.)
Just put your queries in line:
INSERT INTO dsttab (dstfld1, dstfld2)
VALUES (
(SELECT srcfld1
FROM srctab
WHERE srcfld3 ='foo'),
(SELECT srcfld5
FROM srctab
WHERE srcfld6 ='bar')
);
The key point here is to surround the subqueries with parentheses.
I would like to take a list that I have in a text file, of values which are separated by commas:
Example - 1,2,3,4,5,6,7,8,9,0
then put the values in a database table(I'm going to use this table for auto-complete with jQuery).
I would have done an array for the auto-complete but I have something like 1000 values so I think its better to pull from SQL(am i right?)
Try to explain it to me slowly cause I'm a novice and this is so confusing :)
If those are 1000 constant values (like countries), put them in array.
If they are fairly dynamic, put them in a table
Assuming the table is called T1 and has one field F1, you need to transform the string
1,2,3,4,5,6,7,8....N
to
INSERT INTO T1
VALUES (1),(2),(3),(4),(5),(6),(7),(8)......(N);
I have a column that stores data like (42,12). Now I want to fetch 42 or 12 (two different select queries). I have searched and found some similar but much more complex scenarios. Is there any easy way of doing it? I am using MSSQL Server 2005.
Given there will always be only two values and they will be integer
The reason you have this problem is because the database (which you may not have any control over), violates first normal form. Among other things, first normal form says that each column should hold a single value, not multiple values. This is bad design.
Now, having said this, the first solution that pops into my head is to write a UDF that parses the value in this column, based on the delimiter and returns either the first or second value.
You can try something like this
DECLARE #Table TABLE(
Val VARCHAR(50)
)
INSERT INTO #Table (Val) SELECT '42,12'
SELECT *,
CAST(LEFT(Val,CHARINDEX(',',Val)-1) AS INT) FirstValue,
CAST(RIGHT(Val,LEN(Val) - CHARINDEX(',',Val)) AS INT) SecondValue
FROM #Table
You can use something like this:
SELECT SUBSTRING_INDEX(field, ',', 1)
Note: Its not the efficient way of doing things in rdbms. Consider normalizing your Database.