Note that, different SQL implementations support the use of cursors in a different way. A name is given, there are statements to open the cursor, retrieve the query result, and finally close the cursor. Declaring a CursorĬursors are declared much like a variable. Other rows are extracted subsequently, in sequence until the cursor is closed. The cursor then is opened much like a file and extract single row from the query result. As a result, cursor is declared as an embedded SQL statement within the application programming language. The result may contain many rows, but the host application language can deal with one row at a time. The query result from the above statement returns employee details of all those employees whose birth date falls on the current day of a particular month. WHERE MONTH(birth_date) = MONTH(CURRENT_DATE) Consider the following SQL query: SELECT emp_no, first_name, last_name, birth_date A cursor can traverse through all rows of a query result focusing on one row at a time. The cursor, therefore, serves as a pointer that enables programming language to process query result one record at a time. The cursor acts like an iterator variable to loop over tuples returned by the SQL query and extract individual values within each tuple which then can be mapped to appropriate type of program variables. The mechanism of looping over tuples is necessary to iterate over tuples and their attribute values. Therefore, it is essential that SQL query result maps with the data structure supported by the programming language. Host programming languages typically works on individual data values of tuple returned by the query. The result returned by SQL SELECT statements are multi-sets of records where each record is a collection of attributes.Hence a binding mechanism is necessary to mitigate the incompatibility issue. For example, the data types of C/C++ and Java are different and so is SQL data types. There are many host languages, and each have a different data type. The attribute data types available in database model is not the same as the variable types used in programming languages.Therefore, primary mismatch between two models are: columns (or attributes) and their data types. ![]() But here lies the problem of impedance mismatch due to the difference in construct between database model and programming language model.Ī SQL database model has three main constructs: The data elements returned are used by programming languages like Java or any other for specific application purposes. You can scroll through the result sets to extract the information you need. The result sets are nothing but combinations of one or more rows and columns extracted from one or more tables. As a result, query results return by SQL SELECT statements are referred to as result sets. The data in relational database are managed in the form of sets. This article quickly explores the concept behind and show how to declare cursors, open, retrieve data from them, and then close them. VALUES (',rec_tbls.hadm_id,',''',tbl_column,''',''',life_cycle,''',',rec_tbls.In SQL cursors serve as a pointer that enables application programming language to deal with query results one row at a time. (case_id, activity, lifecycle, time_stamp) VALUES (',rec_tbls.hadm_id,',''',tbl_column,''',''',life_cycle,''',',rec_tbls.tbl_column,') ') ĮRROR: record "rec_tbls" has no field "tbl_column"ĬONTEXT: SQL statement "SELECT concat('INSERT INTO EventLog_Main Tx :=concat('INSERT INTO EventLog_Main (case_id, activity, lifecycle, time_stamp) OPEN csr_innner_create_evnt_log FOR EXECUTE sql_eventlog_stge_rows įETCH csr_innner_create_evnt_log INTO tbl_name, tbl_column, col_datatype, event_role, life_cycle OPEN csr_outer_create_evnt_log FOR EXECUTE sql_table_rows įETCH csr_outer_create_evnt_log INTO rec_tbls Set_SrchPath := concat('SET search_path TO ',schem_name,' ') Setting the search path to the specified db schema Sql_table_rows text := 'Select * from admissions ' Sql_eventlog_stge_rows text := 'SELECT tablename, columnname, datatype, eventrole, lifecycle CURSOR CODE BLOCK TO CREATE AN EVENT LOG DOĬsr_outer_create_evnt_log REFCURSOR -Cursor to get the data from the main tableĬsr_innner_create_evnt_log REFCURSOR -Cursor to dissect each row of the main table The problem is, I am passing the value of a column from the returned record from the first cursor but my INSERT statement is not recognizing it. ![]() After evaluating each row, I insert the result to a table ( EventLog_Main). ![]() My plan is to get rows of data from a table ( Admissions) using the "outer cursor" and evaluating each row using criteria from another table ( EventLog_Staging). ![]() I need help with my " postgresql nested cursors" code.
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