Posts (page 70)
-
4 min readTo convert a row_number query to a delete query on PostgreSQL, you can use a common table expression (CTE) to select the rows you want to delete based on the row number. Then, use the DELETE statement with a WHERE clause that references the CTE to delete the selected rows. This allows you to delete specific rows based on their row number without having to manually identify each row by its primary key or another unique identifier.
-
3 min readTo create a pivot table in PostgreSQL, you can use the crosstab function provided by the tablefunc extension. First, you need to install the tablefunc extension by running the following command:CREATE EXTENSION tablefunc;Next, you can use the crosstab function to pivot your data. The crosstab function takes three arguments: the SQL query that returns the source data, the SQL query that defines the row headers, and the SQL query that defines the column headers.
-
5 min readIn PostgreSQL, you can access the function arguments using the pg_proc system catalog. This catalog stores information about all user-defined functions in the database, including their argument types and names. By querying this catalog, you can retrieve the argument types and names of a specific function by specifying its name and namespace. Additionally, you can also use the pg_get_function_arguments function to retrieve the arguments of a specific function.
-
3 min readTo add a subquery to any operator in PostgreSQL, you can use parentheses to group the subquery in conjunction with the operator. The subquery can be used as the right-hand side of the operator to filter the results based on the subquery results. This allows you to customize and refine your query results by incorporating the subquery within the operator logic.
-
5 min readTo create a sequence for integers in PostgreSQL, you can use the command "CREATE SEQUENCE" followed by the name of the sequence and the initial value. For example, to create a sequence named "my_sequence" starting at 1, you can use the following SQL command:CREATE SEQUENCE my_sequence START 1;This will create a sequence that generates integer values starting from 1. You can also specify other parameters such as the increment value and the maximum value for the sequence.
-
6 min readTo import data from a TSV (tab-separated values) file into a PostgreSQL stored procedure, you can first create a temporary table that matches the structure of the data in the TSV file. Then, use the \copy command to load the data from the TSV file into the temporary table within the stored procedure. Once the data is loaded into the temporary table, you can manipulate and process it as needed within the stored procedure logic.
-
3 min readTo convert an interval to the number of seconds in PostgreSQL, you can use the EXTRACT function to extract the seconds from the interval and then do the necessary calculations to convert the interval to seconds. You can also use the DATE_PART function to achieve the same result. By using these functions, you can easily convert intervals to the number of seconds in PostgreSQL for further calculations or comparisons.
-
6 min readTo create a row number with a specific order in PostgreSQL, you can use the ROW_NUMBER() window function along with the ORDER BY clause. This function assigns a unique incremental integer value to each row based on the specified column ordering. By using the PARTITION BY clause in combination with ORDER BY, you can further refine the row numbering within specific groups of data. This allows you to generate customized row numbers according to your desired sequence or criteria in your SQL queries.
-
5 min readTo create a read-only user in Azure PostgreSQL, you can first connect to your PostgreSQL database using a superuser account. Once connected, you can then create a new user with the desired read-only permissions. When creating the user, you will need to specify the appropriate permissions to ensure they only have read access to the database. This can be done by granting the SELECT permission on the desired tables or schemas.
-
5 min readIn PostgreSQL, you can count array elements in a subquery by using the array_agg function along with the array length function. First, use the array_agg function to group the elements of the array into a single array. Then, use the array_length function to get the length of the array, which will give you the count of elements in the array. You can use this in a subquery to count the elements of an array in a more complex query.
-
3 min readTo find the time difference from a JSON field in PostgreSQL, you can use the ->> operator to extract the time values, convert them to timestamps using the ::timestamp function, and then calculate the difference using the EXTRACT function with the EPOCH option. This will give you the time difference in seconds, which you can then convert to the desired time format if needed.[rating:d26bc4cd-f0cb-4e4e-a59e-9289117d8788]How to retrieve duration between two JSON timestamps in PostgreSQL.
-
5 min readTo use the pg_repack extension on Azure PostgreSQL, you first need to connect to your Azure PostgreSQL server using a tool such as pgAdmin or psql. Once connected, you can create a new schema for the pg_repack extension by running the following command:CREATE SCHEMA pg_repack;Next, you need to install the pg_repack extension into the newly created schema.