Initial Commit.
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ZhijuCen
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# DatabaseReadBind
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Moves to the next record and reads data into the structure from it.
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```
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bool DatabaseReadBind(
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int request, // the handle of a request created in DatabasePrepare
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void& struct_object // the reference to the structure for reading the record
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);
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```
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Parameters
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request
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[in] The handle of a request created in [DatabasePrepare()](/en/docs/database/databaseprepare).
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struct_object
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[out] The reference to the structure the data from the current record is to be read to. The structure should only have numerical types and/or strings (arrays are not allowed) as members and cannot be a descendant.
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Return Value
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Return true if successful, otherwise false. To get the error code, use GetLastError(), the possible responses are:
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- ERR_INVALID_PARAMETER (4003) – no table name specified (empty string or NULL);
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- ERR_WRONG_STRING_PARAMETER (5040) – error converting a request into a UTF-8 string;
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- ERR_DATABASE_INTERNAL (5120) – internal database error;
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- ERR_DATABASE_INVALID_HANDLE (5121) – invalid database handle;
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- ERR_DATABASE_EXECUTE (5124) – request execution error;
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- ERR_DATABASE_NO_MORE_DATA (5126) – no table exists (not an error, normal completion).
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Note
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A number of fields in the struct_object structure should not exceed [DatabaseColumnsCount()](/en/docs/database/databasecolumnscount). If the number of fields in the struct_object structure is less than the number of fields in the record, the partial reading is performed. The remaining data can be explicitly obtained using the corresponding [DatabaseColumnText()](/en/docs/database/databasecolumntext), [DatabaseColumnInteger()](/en/docs/database/databasecolumninteger) and other functions.
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Example:
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```
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struct Person
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{
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int id;
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string name;
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int age;
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string address;
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double salary;
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};
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//+------------------------------------------------------------------+
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//| Script program start function |
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//+------------------------------------------------------------------+
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void OnStart()
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{
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int db;
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string filename="company.sqlite";
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//--- open
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db=DatabaseOpen(filename, DATABASE_OPEN_READWRITE | DATABASE_OPEN_CREATE |DATABASE_OPEN_COMMON);
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if(db==INVALID_HANDLE)
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{
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Print("DB: ", filename, " open failed with code ", GetLastError());
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return;
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}
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//--- if the table COMPANY exists then drop the table
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if(DatabaseTableExists(db, "COMPANY"))
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{
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//--- delete the table
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if(!DatabaseExecute(db, "DROP TABLE COMPANY"))
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{
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Print("Failed to drop table COMPANY with code ", GetLastError());
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DatabaseClose(db);
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return;
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}
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}
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//--- create table
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if(!DatabaseExecute(db, "CREATE TABLE COMPANY("
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"ID INT PRIMARY KEY NOT NULL,"
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"NAME TEXT NOT NULL,"
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"AGE INT NOT NULL,"
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"ADDRESS CHAR(50),"
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"SALARY REAL );"))
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{
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Print("DB: ", filename, " create table failed with code ", GetLastError());
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DatabaseClose(db);
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return;
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}
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//--- insert data
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if(!DatabaseExecute(db, "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) VALUES (1, 'Paul', 32, 'California', 25000.00 ); "
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"INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) VALUES (2, 'Allen', 25, 'Texas', 15000.00 ); "
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"INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );"
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"INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );"))
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{
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Print("DB: ", filename, " insert failed with code ", GetLastError());
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DatabaseClose(db);
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return;
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}
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//--- prepare the request
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int request=DatabasePrepare(db, "SELECT * FROM COMPANY WHERE SALARY>15000");
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if(request==INVALID_HANDLE)
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{
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Print("DB: ", filename, " request failed with code ", GetLastError());
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DatabaseClose(db);
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return;
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}
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//--- print records
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Person person;
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Print("Persons with salary > 15000:");
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for(int i=0; DatabaseReadBind(request, person); i++)
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Print(i, ": ", person.id, " ", person.name, " ", person.age, " ", person.address, " ", person.salary);
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//--- delete request after use
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DatabaseFinalize(request);
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Print("Some statistics:");
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//--- prepare new request about total salary
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request=DatabasePrepare(db, "SELECT SUM(SALARY) FROM COMPANY");
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if(request==INVALID_HANDLE)
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{
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Print("DB: ", filename, " request failed with code ", GetLastError());
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DatabaseClose(db);
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return;
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}
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while(DatabaseRead(request))
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{
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double total_salary;
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DatabaseColumnDouble(request, 0, total_salary);
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Print("Total salary=", total_salary);
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}
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//--- delete request after use
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DatabaseFinalize(request);
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//--- prepare new request about average salary
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request=DatabasePrepare(db, "SELECT AVG(SALARY) FROM COMPANY");
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if(request==INVALID_HANDLE)
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{
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Print("DB: ", filename, " request failed with code ", GetLastError());
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ResetLastError();
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DatabaseClose(db);
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return;
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}
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while(DatabaseRead(request))
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{
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double aver_salary;
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DatabaseColumnDouble(request, 0, aver_salary);
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Print("Average salary=", aver_salary);
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}
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//--- delete request after use
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DatabaseFinalize(request);
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//--- close database
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DatabaseClose(db);
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}
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//+-------------------------------------------------------------------
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/*
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Output:
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Persons with salary > 15000:
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0: 1 Paul 32 California 25000.0
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1: 3 Teddy 23 Norway 20000.0
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2: 4 Mark 25 Rich-Mond 65000.0
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Some statistics:
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Total salary=125000.0
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Average salary=31250.0
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*/
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```
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See also
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[DatabasePrepare](/en/docs/database/databaseprepare), [DatabaseRead](/en/docs/database/databaseread)
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