I'm using PostgreSQL server on my Windows.
I have created table user(id, name, age) and inserted some data there.
When I'm trying to retrieve that data via SELECT ALL FROM user I'm getting only the rows count and just plain nothingness.
How it looks like in psql CLI:
...and I'm also receiving empty object array as query result in my nodejs app:
Postgres supports SELECT ALL as a synonym for SELECT -- as a two words syntax parallel to SELECT DISTINCT. The ALL does nothing.
In addition, Postgres -- unlike other databases -- allows a SELECT to select no columns.
So:
SELECT ALL
FROM user;
Selects all the rows from user but no columns. In general, you would instead write:
SELECT *
FROM user;
to see the contents of the rows. If you want to be verbose, yo could use:
SELECT ALL *
FROM user;
But that is used somewhere close to never in practice.
You specified that you want the data from the column named "all". To get data from all columns you need to specify them all or use the asterisk symbol like so:
SELECT * FROM "user";
Related
I have a table named Posts I would like to count and profile in Snowflake using the current Snowsight UI.
When I return the results via EXPLAIN using TABLULAR I am able to return the set with the combination of TABLE, RESULT_SCAN, and LAST_QUERY_ID functions, but any predicate or filter or column reference seems to fail.
Is there a valid way to do this in Snowflake with the TABLE function or is there another way to query the output of the EXPLAIN using TABLULAR?
-- Works
EXPLAIN using TABULAR SELECT COUNT(*) from Posts;
-- Works
SELECT t.* FROM TABLE(RESULT_SCAN(LAST_QUERY_ID())) as t;
-- Does not work
SELECT t.* FROM TABLE(RESULT_SCAN(LAST_QUERY_ID())) as t where operation = 'GlobalStats';
-- invalid identifier 'OPERATION', the column does not seem recognized.
Tried the third example and expected the predicate to apply to the function output. I don't understand why the filter works on some TABLE() results and not others.
You need to double quote the column name
where "operation"=
From the Documentation
Note that because the output column names from the DESC USER command
were generated in lowercase, the commands use delimited identifier
notation (double quotes) around the column names in the query to
ensure that the column names in the query match the column names in
the output that was scanned
I've been using the LIST command to check the files staged to a table in Snowflake. However, the data is unordered and I'd like to order it by last_modified. I tried embedding it into a SELECT query like this:
SELECT *
FROM LIST #MY_DATABASE.MY_SCHEMA.%my_table/path/to/data PATTERN = '.*[.]csv.*'
However, this query fails to compile. I've tried preceding LIST with the CALL keyword as well, but no luck there. I've even tried assigning it to a local variable, but that doesn't work either. The data appears to be tabular so I'm not sure why I can't work with it.
How can I query on the output of LIST?
I am personally using the following "hacky" solution:
Start by executing the "list" command.
I Then use the result_scan function combined with last_query_id function to fetch the results of that query, as this point I can start querying the data, here's how it looks:
LIST #MY_DATABASE.MY_SCHEMA.%my_table/path/to/data PATTERN = '.*[.]csv.*'
WITH data(name, size, md5, last_modified) as (
SELECT * FROM table(result_scan(last_query_id()))
)
select *
from data
order by last_modified desc;
Obviously this is a manual hack as I retrieve the last query id, if you can't ensure this property you need to get the actual query id and use that explicitly instead.
it looks that SqlQuery only supports sql that starts with select *? Doesn't it support other sql that only select some columns like
select id, name from person and maps the columns to the corresponding POJO?
If I use SqlFieldQuery to run sql, the result is a QueryCursor of List(each List contains one record of the result). But if the sql starts with select *, the this list's contents would be different with field query like:
select id,name,age from person
For the select *, each List is constructed with 3 parts:
the first elment is the key of the cache
the second element is the pojo object that contains the data
the tailing element are the values for each column.
Why was it so designed? If I don't know what the sql that SqlFieldsQuery runs , then I need additional effort to figure out what the List contains.
SqlQuery returns key and value objects, while SqlFieldsQuery allows to select specific fields. Which one to use depends on your use case.
Currently select * indeed includes predefined _key and _val fields, and this will be improved in the future. However, generally it's a good practice to list fields you want to fetch when running SQL queries (this is true for any SQL database, not only Ignite). This way your code will be protected from unexpected behavior in case schema is changed, for example.
How can I select the column name and table name from a SQL?
I tried something like this but it didn't work:
select column_name, table_name from (select * from users);
This might sound silly, but I have a list of different SQLs and I need to extract their columns and tables into a list. So some of the statements could me:
select username, password from users
select createdate from userlog
select * from dept
...
If I can select the column name and table name of a select statement, then I should get, say for the first statement, username and password for columns and users for table name. And createdate for column and userlog for table name in the second statement.
Then if it all works, I can then loop through the list of select statements and extract their column and table names.
The below query worked for Oracle database.
SELECT COLUMN_NAME,TABLE_NAME FROM ALL_TAB_COLUMNS
You can see more about information-schema
Edit:
You may try like this:
SELECT COLUMN_NAME,TABLE_NAME FROM ALL_TAB_COLUMNS
WHERE TABLE_NAME IN (SELECT ColumnName FROM users)
You need to parse the SQL statement so the SQL engine figures out the columns and datatypes of the columns that the statement returns.
How you do it best depends on what environment you are using. In some programming languages when you create a SqlPreparedStatement or OraCommand or whatever the object may be called, that object may have a metadata collection populated with column information after parsing.
If you are doing it in the database itself, parsing your statement with DBMS_SQL can get you the information you need. See Example 8 in the documentation at this link:
http://docs.oracle.com/database/121/ARPLS/d_sql.htm#ARPLS68205
--
Oh, and this gives you column names of the select statement. The table names I do not know of any way to get easily.
I have a unique column. I also have a known set of elements that are possible values for the column. I need to know which of the possible values are not already in the table, and as such, are suitable for insertion.
Is this possible with SQL or is post processing required?
Currently, I am using the "in" operator to select all rows where the column value equals an element in my set. Then I remove all matched elements from my set via post processing.
Stick the allowed values in a temporary table allowed, then use a subquery using NOT IN:
SELECT *
FROM allowed
WHERE allowed.val NOT IN (
SELECT maintable.val
)
Some DBs will allow you to build up a table "in-place", instead of having to create a separate table. E.g. in PostgreSQL (any version):
SELECT *
FROM (
SELECT 'foo'
UNION ALL SELECT 'bar'
UNION ALL SELECT 'baz' -- etc.
) inplace_allowed
WHERE inplace_allowed.val NOT IN (
SELECT maintable.val
)
More modern versions of PostgreSQL (and perhaps other DBs) will let you use the slightly nicer VALUES syntax to do the same thing.
To do this entirely in SQL you will need to create a separate table with one column. Each row holds one value from the known set of elements. Assuming the table is called ElementList and the other table is called Existing:
SELECT * FROM ElementList WHERE Element NOT IN
(SELECT DISTINCT Element FROM Existing)
Depending on what database engine you're using you may be able to use a temporary table to create and hold the list without saving it permanently in the database. However, storing the list of allowed elements is valuable for constraining the Element column in the Existing table (and for presenting the user with allowed Elements in the user interface).