Commonly used query methods and techniques in Golang

In recent years, Golang has become more and more popular in the field of backend development, and many companies have begun to use Golang to build their own applications. However, during the development process, there are some difficulties that we need to face and solve. How to query efficiently is an important issue. This article will introduce common query methods and techniques in Golang to help you solve this problem more easily.

1. Query from arrays and slices

1.1 Traversal query

The most basic and common query method is to traverse the array or slice, use a for loop to traverse the elements one by one and perform Compare. Although this method can complete the query operation, the query speed is relatively slow, especially when the amount of data is large, the efficiency will be even lower.

1.2 Binary search

Binary search is an efficient query method, suitable for ordered arrays or slices. It continuously compares the intermediate value with the target value, and then gradually narrows the query range to finally find the target value.

The following is a sample code for binary search:

func binarySearch(nums []int, target int) int {
    left, right := 0, len(nums)-1
    
    for left <= right {
        mid := (left + right) / 2
        
        if nums[mid] == target {
            return mid
        } else if nums[mid] < target {
            left = mid + 1
        } else {
            right = mid - 1
        }
    }
    
    return -1
}

1.3 Query using map

Map is an associative data type in Golang, similar to a dictionary in Python. It can quickly find the corresponding value based on the key, so it is very suitable for query operations.

The following is a sample code for querying using map:

func lookup(nums []int, target int) bool {
    mp := make(map[int]bool)
    
    for _, num := range nums {
        mp[num] = true
    }
    
    return mp[target]
}

2. Query from the database

In practical applications, we often need to query data from the database. There are a variety of database operation libraries in Golang, such as database/sql, gorm, etc., and they all provide corresponding query methods.

2.1 Query using database/sql

database/sql is the default database operation library in Golang. It supports a variety of relational databases, such as MySQL, PostgreSQL, SQLite, etc.

The following is a sample code for querying using database/sql:

import (
    "database/sql"
    "fmt"
    _ "github.com/go-sql-driver/mysql"
)

func query() {
    db, err := sql.Open("mysql", "USER:PASSWORD@/DATABASENAME")
    if err != nil {
        panic(err.Error())
    }
    defer db.Close()

    rows, err := db.Query("SELECT * FROM mytable")
    if err != nil {
        panic(err.Error())
    }
    defer rows.Close()

    for rows.Next() {
        var id int
        var name string
        if err := rows.Scan(&id, &name); err != nil {
            panic(err.Error())
        }
        fmt.Println(id, name)
    }
}

2.2 Querying using gorm

gorm is a powerful ORM (Object Relational Mapping) library , providing good query interfaces and functions, which can help developers operate the database more conveniently.

The following is a sample code using gorm for query:

import (
    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/mysql"
)

type User struct {
    ID   int
    Name string
    Age  int
}

func main() {
    db, err := gorm.Open("mysql", "USER:PASSWORD@/DATABASENAME?charset=utf8&parseTime=True&loc=Local")
    if err != nil {
        panic(err)
    }
    defer db.Close()

    var users []User
    db.Where("age > ?", 18).Find(&users)

    for _, user := range users {
        fmt.Println(user.ID, user.Name, user.Age)
    }
}

3. Summary

When using Golang for query, we can use traversal, binary search, and map Query using other methods. For querying from the database, database/sql and gorm are two commonly used libraries. They both provide query interfaces and functions. Developers can choose the appropriate library to operate according to their needs.

No matter which query method is used, you need to pay attention to query efficiency and performance, reduce unnecessary traversal operations as much as possible, and improve query efficiency.

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