Database Management Systems
In SQLite, the json_patch() function can be used to add, modify, or delete elements of a JSON Object.
To do this, it runs the RFC-7396 MergePatch algorithm to apply a given patch against the given JSON input.
We pass the original JSON as the first argument when we call the function, followed by the patch. The function then applies that patch against JSON in the first argument.
If you’re getting an error that reads “ERROR 3942 (HY000): Each row of a VALUES clause must have at least one column” in MySQL, you could have an empty row constructor when using the VALUES statement.
To fix this issue, make sure you’ve got at least one value in each ROW() clause within the VALUES statement.
The SQLite json_replace() function allows us to replace an existing value in a JSON document with another value.
We pass the original JSON as the first argument when we call the function, followed by the path of the value to replace, followed by the value to replace.
We can also replace multiple key/value pairs if required.
The SQLite json_set() function allows us to insert into, or replace, a value in a JSON document.
We pass the original JSON as the first argument when we call the function, followed by a path that specifies where to insert/replace the new value, followed by the value to insert/replace.
We can also insert/replace multiple key/value pairs if required.
The following examples use T-SQL to delete duplicate rows in SQL Server while ignoring the primary key or unique identifier column.
More specifically, the examples delete duplicate rows but keep one. So, given two identical rows, one is deleted and the other remains. This is often referred to as “de-duping” the table, “deduplication” of the table, etc.
The SQLite json_insert() function allows us to insert a new value into a JSON document.
We pass the original JSON as the first argument when we call the function, followed by a path that specifies where to insert the new value, followed by the value to insert.
We can also insert multiple key/value pairs if required.
In SQLite, the json_extract() function extracts and returns one or more values from well-formed JSON.
We pass the JSON as an argument when we call the function, and it returns the applicable value/s.
We can specify one or more paths to extract from the JSON document.
When using the UNION operator in MariaDB, you may encounter the following error: “ERROR 1222 (21000): The used SELECT statements have a different number of columns”.
This error occurs when the number of columns returned by each SELECT statement is different.
The way to fix this is to ensure that both SELECT statements return the same number of columns.
In PostgreSQL, we can use the + operator to add one or more years to a date.
In SQLite, the json_array_length() function returns the number of elements in a given JSON array.
The array is provided as an argument. If the array is embedded within a larger JSON document, we can use an optional second argument to specify the path to the array.
If the value is not an array, the function returns 0.