Posts (page 72)
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4 min readIn PostgreSQL, you can apply a limit conditionally by using a CASE statement in your query. The CASE statement allows you to define different conditions and return different results based on those conditions.For example, if you only want to limit the number of results if a certain condition is met, you can use a CASE statement to check for that condition. If the condition is met, you can apply the limit using the LIMIT keyword.
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5 min readIn PostgreSQL's EXPLAIN ANALYZE feature, "unique" refers to the use of a unique index to enforce uniqueness in a table. When a query involves accessing a unique index to retrieve data, the "unique" keyword will appear in the EXPLAIN ANALYZE output. This indicates that PostgreSQL is using a unique index to efficiently retrieve and filter the data requested by the query.
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4 min readTo parse serialized JSON in PostgreSQL, you can use the json_populate_record function to convert a JSON object into a record type, json_populate_recordset to convert a JSON array into a set of records, or the jsonb_to_record function to convert a JSONB object into a record type. You can also use the json_extract_path_text function to extract specific values from a JSON object using JSONPath.
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4 min readTo get a specific key from a JSONB column in PostgreSQL, you can use the -> operator followed by the key name you want to extract.For example, if you have a JSONB column named data in a table named json_data, and you want to extract the value of a key named name, you can use the following query: SELECT data->'name' FROM json_data; This will return the value associated with the key name from the JSONB column data in the json_data table.
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5 min readTo execute a PostgreSQL function at a specific time interval, you can use the pg_cron extension, which allows you to schedule jobs directly within the database. This extension integrates cron-like scheduling capabilities into PostgreSQL, making it easy to run functions at predetermined times.First, you need to install the pg_cron extension by running the appropriate SQL script on your database.
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4 min readTo loop through JSON attributes in PostgreSQL, you can use the json_each_text function along with a LATERAL join. This function allows you to unnest a JSON object and return each key-value pair as a separate row. You can then access the key and value attributes in your query to manipulate the data as needed. This can be particularly useful when working with JSON data in PostgreSQL and needing to iterate over the attributes of a JSON object.
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6 min readIn PostgreSQL, you can compare and take non-duplicate text by using the DISTINCT keyword in combination with the SELECT statement. This allows you to retrieve unique values from a column or set of columns in a table.
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7 min readTo insert a comma separated document into PostgreSQL, you will first need to ensure that the table you are inserting the data into has the necessary columns to store the information from the document. You can then use the COPY command in PostgreSQL to load the comma separated document into the table. The COPY command allows you to read data from a file and insert it into a table in bulk.
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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.
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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.
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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.
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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.