golang query with different conditions

As Golang is used more and more widely in enterprise-level applications, querying data has also become an important requirement. It is different from the way of querying in other languages. This article will introduce how to use Golang to query with different conditions.

Types of Golang

In Golang, there are different data types available, mainly including:

• string: String type
• int: Integer type
• float: Floating point type
• bool: Boolean type
• struct: Structure type

for different data Type, we can use different query methods.

Single condition query

Single condition query is the simplest query method and the most common one. For example, we need to query students who are 18 years old from a student list.

type Student struct {
    Name string
    Age  int
}
var students []Student
// 初始化students
for _, student := range students {
    if student.Age == 18 {
        fmt.Println(student.Name)
    }
}

Just define a structure type Student, and then find students whose age is equal to 18 in the loop.

If we need to retrieve a field of string type, we can use the strings.HasPrefix or strings.HasSuffix function. For example, to query a movie list for movies whose names start with "Harry Potter":

type Movie struct {
    Name string
    Year int
}
var movies []Movie
// 初始化movies
for _, movie := range movies {
    if strings.HasPrefix(movie.Name, "Harry Potter") {
        fmt.Println(movie.Name)
    }
}

Using the strings.HasPrefix function and branch conditional statements (if statements), we can find these movies.

Multi-condition query

Multi-condition query needs to consider multiple different fields to return a result. For example, if we have a list of orders, we need to retrieve orders for a specific date and for a specific customer.

type Order struct {
    OrderID    int
    CustomerID int
    Date       time.Time
}
var orders []Order
// 初始化orders
for _, order := range orders {
    if order.CustomerID == 123 && order.Date == time.Date(2021, 1, 1, 0, 0, 0, 0, time.Local) {
        fmt.Println(order.OrderID)
    }
}

In the above example, we used the logical operator && to check whether two conditions are true at the same time.

Range query

In some cases, we need to query data within a range, which requires the use of comparison operators. For example, query a student whose grades are between 80 and 90:

type Score struct {
    Name  string
    Grade float64
}
var scores []Score
// 初始化scores
for _, score := range scores {
    if score.Grade >= 80 && score.Grade < 90 {
        fmt.Println(score.Name)
    }
}

In the above example, we used the >= and < comparison operators because we need to query between 80 and 90 scores, excluding 90.

Fuzzy query

Fuzzy query is a very common query method, usually used to search for data that contains specific characters or strings in the string. For example, query a movie list for movies that contain the string "Avengers":

type Movie struct {
    Name string
    Year int
}
var movies []Movie
// 初始化movies
for _, movie := range movies {
    if strings.Contains(movie.Name, "Avengers") {
        fmt.Println(movie.Name)
    }
}

In the above example, we used the strings.Contains function to check whether the string contains the specified substring.

Other query methods

In addition to the above methods, Golang also provides more query methods, such as using regular expression matching, using map to query data, etc. Depending on different needs and data types, we can choose different query methods.

Conclusion

This article introduces different query methods in Golang, including single-condition query, multi-condition query, range query, fuzzy query, etc. Understanding these query methods can help us use Golang to query and process data more efficiently.

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