The question mark in the SQL statement learning notes

I see an instance of

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String sql = "Select Userid,name from Tuser WHERE userid=?" and password=? "; pstmt = conn.preparestatement (sql); Pstmt.setstring (1,userid); Set the first one here? The value Pstmt.setstring (2,password); The second one is set here? The value

After you "setstring" all of this? , your SQL is built up.

Well, if I still don't understand, I've found another article.

Reference I:

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SELECT * FROM table where username= ' syy913 ' Username= ' syy913 '

followed by a string. In the database is used when the quotation marks. There is a mantra called both Gaga alone.

Used only in the database, the dual is used in the external programming language, in C # Java and other languages are used in the double quotes identified by the string.

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String Sql= "select * from table", which identifies a string. String Sql= "select * FROM table" + "where id>0″;2 string connection

Below the

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String Sql= "select * from table where id>0″+" and name=?;

This question mark indicates the parameter to pass. The parameter must be given to him before executing this SQL, and the name above is character-type. You're looking at what it means to write.

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String nn= "Kill" String Sql= "select * from table where id>0 and name=?";

Because? represents a string.

The nn output to see he is not "" this.

Then it should be ' nn ' to the database, i.e.

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String Sql= "select * from table where id>0 and name= ' nn '";

On it, why do you want the inside + double quotes?

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String Sql= "select * from table where id>0 and Name= '" +nn+ "";

I gave him nn as a variable.

Reference II:

This SQL statement can be used with a question mark ("?") if it contains parameters. To take a placeholder for a parameter without immediately assigning a value to the parameter, and before the statement executes, you must assign a value to the argument at the question mark by the appropriate set*** (). In New Parseinfo (), the SQL statement that contains the parameters is decomposed into multiple segments and placed in Staticsql so that the position of the parameter is required when the parameter is set. Suppose the SQL statement is "SELECT * from adv where id =?" and name =? " , then the elements in Staticsql are 3, staticsql[3]={"select * from adv WHERE id =", "and name =", ""}. Note that the last element in the array, in this case, is "", because the last one in my example is "?", if the SQL statement is such "select * from adv where id =?" and name =? Order by ID, Staticsql becomes this way {"SELECT * from adv WHERE id =", "and name =", "ORDER by id"}.

Irrelevant reference three: (MySQL manual C API preprocessing statements)

25.2.7.4. Mysql_stmt_bind_param ()

My_bool Mysql_stmt_bind_param (mysql_stmt *stmt, Mysql_bind *bind)

Describe

Mysql_stmt_bind_param () is used to bind data to a parameter marker in an SQL statement to pass to Mysql_stmt_prepare (). It uses the MYSQL_BIND structure to provide data. "Bind" is the address of an array of mysql_bind structures. As expected by the client library, for each "?" that appears in the query. Parameter markers that contain 1 elements in the array.

Suppose you prepared the following statement:

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INSERT into Mytbl VALUES (?,?,?) When binding parameters, an array of mysql_bind structures contains 3 elements and can be declared as follows: Mysql_bind Bind[3];