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Let us understand what user variables are and how they can be used in MySQL. We will also see the rules −User variables are written as @var_name. Here, the ‘var_name’ refers to variable name, which consists of alphanumeric characters, ., _, and $.A user variable name can contain other characters if they are quoted as a string or identifier.User-defined variables are session specific.A user variable which is defined by one client can’t be seen or used by other clients.But the only exception is that if a user has access to the Performance Schema user_variables_by_thread table, then that user can see ... Read More
Let us understand how to find the rows that hold the group wise maximum of a specific column in MySQL −The syntax to find the rows that hold the group-wise maximum of a specific column in MySQL is as follows −SELECT colName1, colName2, colName3 FROM tableName s1 WHERE colName3=(SELECT MAX(s2. colName3) FROM tableName s2 WHERE s1. colName1= s2. colName1) ORDER BY colName1;Let’s say we have the following PRODUCT Table −+---------+----------+--------+ | Article | Warehouse| Price | +---------+----------+--------+ | 1 | North | 255.50 | | 1 | North | 256.05 | | ... Read More
Let us understand how to find the maximum of a column per group in MySQL −SELECT colName1, MAX(colName2) FROM tableName GROUP BY colName1 ORDER BY colName1;We will now see a live example. Let’s say we have a table PRODUCT −+---------+--------+ | Article | Price | +---------+--------+ | 1 | 255.50 | | 1 | 256.05 | | 2 | 90.50 | | 3 | 120.50 | | 3 | 123.10 | | 3 | 122.10 | +---------+--------+Following is the query to get the maximum of column per group −QuerySELECT Article, MAX(Price) AS MaxPrice FROM Product GROUP BY Article ORDER BY Article;Output+--------------+--------------+ | Article | MaxPrice | +--------------+--------------+ | 0001 | 256.05 | | 0002 | 90.50 | | 0003 | 123.10 | +--------------+--------------+
Files is collection of records (or) it is a place on hard disk, where data is stored permanently. By using C commands, we access the files in different ways.Need of files in C languageEntire data is lost when the program terminates and storing in a file will preserve your data even if the program terminates.If you want to enter a large amount of data, normally, it takes a lot of time to enter them all.If you have a file containing all the data, you can easily access the contents of the file by using few commands in C.You can easily ... Read More
A union is called as a memory location, which is shared by several variables of different data types.SyntaxThe syntax is as follows −union uniontag{ datatype member 1; datatype member 2; ---- ---- datatype member n; };For example, union sample{ int a; float b; char c; };Declaration of union variableGiven below are the respective declarations of union variable −Union sample{ int a; float b; char c; }s;Union{ int a; float b; char c; }s;Union sample{ int a; float b; char c; }; union sample ... Read More
If the structure is nested inside a union, it is called as a union of structures. There is a possibility to create a union inside a structure in C programming language.ExampleFollowing is the C program for union of structures −#include struct x { int a; float b; }; union z{ struct x s; }; main ( ){ union z u; u.s.a = 10; u.s.b = 30.5; printf("a=%d", u.s.a); printf("b=%f", u.s.b); getch ( ); }OutputWhen the above program is executed, it produces the following result −a= 10 b = 30.5ExampleGiven below is ... Read More
Structure is a collection of different datatype variables, grouped together under a single name.Features of structureThe features of structure are explained below −It is possible to copy the contents of all structure elements of different datatypes to another structure variable of its type by using an assignment operator.For handling complex datatypes, it is better to create a structure within an another structure, which is called as the nested structures.It is possible to pass an entire structure, individual elements of a structure and an address of structure to a function.It is also possible to create the structure pointers.Declaration of structuresThe general ... Read More
ProblemIn C language, is the program executed, if we use an uninitialized array?SolutionIf we use any uninitialized array, compiler will not generate any compilation and an execution error.If an array is uninitialized, you may get unpredictable result.So, it’s better we should always initialize the array elements with default values.Example ProgramFollowing is the C program of accessing an uninitialized array − Live Demo#include int main(void){ int a[4]; int b[4] = {1}; int c[4] = {1,2,3,4}; int i; //for loop counter //printing all alements of all arrays printf("Array a:"); for( i=0; i
Suppose you have an array with four elements. Then, an array indexing will be from 0 to 3, i.e., we can access elements from index 0 to 3.But, if we use index which is greater than 3, it will be called as an index out of bounds.If, we use an array index which is out of bounds, then the compiler will compile and even run. But, there is no guarantee for the correct result.Result can be not sure and it will start causing many problems. Hence, it is advised to be careful while using an array indexing.Example ProgramFollowing is the ... Read More
Pointer to structure holds the address of an entire structure.Mainly, these are used to create the complex data structures such as linked lists, trees, graphs and so on.The members of the structure can be accessed by using a special operator called arrow operator ( -> ).DeclarationFollowing is the declaration for pointer to structure −struct tagname *ptr;For example, struct student *s;AccessingYou can access pointer to structure by using the following −Ptr-> membername;For example, s->sno, s->sname, s->marks;ExampleFollowing is the C program of the pointer structures −#include struct student{ int sno; char sname[30]; float marks; }; main ( ){ ... Read More