【原創】mysql優化

1：當只要一行數據時使用 LIMIT 1

當你查詢表的有些時候，你已經知道結果只會有一條結果，但由於你可能須要去fetch遊標，或是你也許會去檢查返回的記錄數。
在這種狀況下，加上 LIMIT 1 能夠增長性能。這樣同樣，MySQL數據庫引擎會在找到一條數據後中止搜索，而不是繼續日後查少下一條符合記錄的數據。

[mw_shl_code=applescript,true]SELECT * FROM user WHERE country = 'China'
 
SELECT 1 FROM user WHERE country = 'China' LIMIT 1

[/mw_shl_code]
假如你這邊只是爲了，查詢有沒有中國用戶存在，那麼第二句，效率明顯高於第一句。
2：給平凡查詢的字段加索引，爲了測試先來建立一張表往裏面添加100000條記錄

CREATE TABLE users(
name VARCHAR(10),
id INT
);

插入數據的代碼

public class Cp30Demo {
 
    public static void main(String[] args) {
        try {
            DataSource dataSource = new ComboPooledDataSource();
            Connection con = dataSource.getConnection();
            con.setAutoCommit(false);
 
            PreparedStatement psm = con.prepareStatement("INSERT  INTO users(name,id) value(?,?)");
            for (int i = 0; i < 5000000; i++) {
                psm.setString(1,getRandomString2(5));
                psm.setString(2,i+"");
                psm.addBatch();//添加到批次
            }
            psm.executeBatch();//提交批處理
            con.commit();//執行
            con.close();
        }catch (Exception e){
        e.printStackTrace();}
    }
 
 
 
    public static String getRandomString2(int length){
        Random random=new Random();
        StringBuffer sb=new StringBuffer();
        for(int i=0;i<length;i++){
            int number=random.nextInt(3);
            long result=0;
            switch(number){
                case 0:
                    result=Math.round(Math.random()*25+65);
                    sb.append(String.valueOf((char)result));
                    break;
                case 1:
                    result=Math.round(Math.random()*25+97);
                    sb.append(String.valueOf((char)result));
                    break;
                case 2:
                    sb.append(String.valueOf(new Random().nextInt(10)));
                    break;
            }
        }
        return sb.toString();
    }
    @Test
    public void testindex(){
        try {
            DataSource dataSource = new ComboPooledDataSource();
            Connection con = dataSource.getConnection();
            PreparedStatement psm = con.prepareStatement("SELECT * FROM users WHERE name='vC'");
            long l = System.currentTimeMillis();
            boolean execute = psm.execute();
            System.out.println(System.currentTimeMillis()-l);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
 
 
 
    }

在建索引以前

@Test
public void testindex(){
    try {
        DataSource dataSource = new ComboPooledDataSource();
        Connection con = dataSource.getConnection();
        PreparedStatement psm = con.prepareStatement("SELECT * FROM users WHERE name='vcpwT'");
        long l = System.currentTimeMillis();
        boolean execute = psm.execute();
        System.out.println(System.currentTimeMillis()-l);
    } catch (SQLException e) {
        e.printStackTrace();
    }
}

運行結果

C:\java8\bin\java.exe -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\lib\idea_rt.jar=2938:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\lib\idea_rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\plugins\junit\lib\junit-rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\plugins\junit\lib\junit5-rt.jar;C:\java8\jre\lib\charsets.jar;C:\java8\jre\lib\deploy.jar;C:\java8\jre\lib\ext\access-bridge-64.jar;C:\java8\jre\lib\ext\cldrdata.jar;C:\java8\jre\lib\ext\dnsns.jar;C:\java8\jre\lib\ext\jaccess.jar;C:\java8\jre\lib\ext\jfxrt.jar;C:\java8\jre\lib\ext\localedata.jar;C:\java8\jre\lib\ext\nashorn.jar;C:\java8\jre\lib\ext\sunec.jar;C:\java8\jre\lib\ext\sunjce_provider.jar;C:\java8\jre\lib\ext\sunmscapi.jar;C:\java8\jre\lib\ext\sunpkcs11.jar;C:\java8\jre\lib\ext\zipfs.jar;C:\java8\jre\lib\javaws.jar;C:\java8\jre\lib\jce.jar;C:\java8\jre\lib\jfr.jar;C:\java8\jre\lib\jfxswt.jar;C:\java8\jre\lib\jsse.jar;C:\java8\jre\lib\management-agent.jar;C:\java8\jre\lib\plugin.jar;C:\java8\jre\lib\resources.jar;C:\java8\jre\lib\rt.jar;C:\Users\yqw\Desktop\jiuye\out\production\jiuye;C:\Users\yqw\Desktop\jiuye\lib\c3p0-0.9.5.2.jar;C:\Users\yqw\Desktop\jiuye\lib\druid-1.0.9.jar;C:\Users\yqw\Desktop\jiuye\lib\mchange-commons-java-0.2.12.jar;C:\Users\yqw\Desktop\jiuye\lib\mysql-connector-java-5.1.37-bin.jar;C:\Users\yqw\Desktop\jiuye\lib\c3p0-0.9.5.2-sources.jar;C:\Users\yqw\.m2\repository\junit\junit\4.12\junit-4.12.jar;C:\Users\yqw\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit4 com.itheima._04cp3o.Cp30Demo,testindex
六月 15, 2019 9:24:27 上午 com.mchange.v2.log.MLog 
信息: MLog clients using java 1.4+ standard logging.
六月 15, 2019 9:24:28 上午 com.mchange.v2.c3p0.C3P0Registry 
信息: Initializing c3p0-0.9.5.2 [built 08-December-2015 22:06:04 -0800; debug? true; trace: 10]
六月 15, 2019 9:24:28 上午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource 
信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 5000, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, dataSourceName -> 1hgerr5a3omcukmg48chl|65e579dc, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, extensions -> {}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, forceUseNamedDriverClass -> false, identityToken -> 1hgerr5a3omcukmg48chl|65e579dc, idleConnectionTestPeriod -> 0, initialPoolSize -> 10, jdbcUrl -> jdbc:mysql://192.168.136.128:3306/day17, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {user=******, password=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ]
1832

添加索引

ALTER TABLE `users` ADD UNIQUE INDEX `name` (`name`) USING BTREE

運行結果

C:\java8\bin\java.exe -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\lib\idea_rt.jar=3083:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\lib\idea_rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\plugins\junit\lib\junit-rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.2\plugins\junit\lib\junit5-rt.jar;C:\java8\jre\lib\charsets.jar;C:\java8\jre\lib\deploy.jar;C:\java8\jre\lib\ext\access-bridge-64.jar;C:\java8\jre\lib\ext\cldrdata.jar;C:\java8\jre\lib\ext\dnsns.jar;C:\java8\jre\lib\ext\jaccess.jar;C:\java8\jre\lib\ext\jfxrt.jar;C:\java8\jre\lib\ext\localedata.jar;C:\java8\jre\lib\ext\nashorn.jar;C:\java8\jre\lib\ext\sunec.jar;C:\java8\jre\lib\ext\sunjce_provider.jar;C:\java8\jre\lib\ext\sunmscapi.jar;C:\java8\jre\lib\ext\sunpkcs11.jar;C:\java8\jre\lib\ext\zipfs.jar;C:\java8\jre\lib\javaws.jar;C:\java8\jre\lib\jce.jar;C:\java8\jre\lib\jfr.jar;C:\java8\jre\lib\jfxswt.jar;C:\java8\jre\lib\jsse.jar;C:\java8\jre\lib\management-agent.jar;C:\java8\jre\lib\plugin.jar;C:\java8\jre\lib\resources.jar;C:\java8\jre\lib\rt.jar;C:\Users\yqw\Desktop\jiuye\out\production\jiuye;C:\Users\yqw\Desktop\jiuye\lib\c3p0-0.9.5.2.jar;C:\Users\yqw\Desktop\jiuye\lib\druid-1.0.9.jar;C:\Users\yqw\Desktop\jiuye\lib\mchange-commons-java-0.2.12.jar;C:\Users\yqw\Desktop\jiuye\lib\mysql-connector-java-5.1.37-bin.jar;C:\Users\yqw\Desktop\jiuye\lib\c3p0-0.9.5.2-sources.jar;C:\Users\yqw\.m2\repository\junit\junit\4.12\junit-4.12.jar;C:\Users\yqw\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit4 com.itheima._04cp3o.Cp30Demo,testindex
六月 15, 2019 9:26:35 上午 com.mchange.v2.log.MLog 
信息: MLog clients using java 1.4+ standard logging.
六月 15, 2019 9:26:35 上午 com.mchange.v2.c3p0.C3P0Registry 
信息: Initializing c3p0-0.9.5.2 [built 08-December-2015 22:06:04 -0800; debug? true; trace: 10]
六月 15, 2019 9:26:35 上午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource 
信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 5000, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, dataSourceName -> 1hgerr5a3omfkzeukux9|65e579dc, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, extensions -> {}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, forceUseNamedDriverClass -> false, identityToken -> 1hgerr5a3omfkzeukux9|65e579dc, idleConnectionTestPeriod -> 0, initialPoolSize -> 10, jdbcUrl -> jdbc:mysql://192.168.136.128:3306/day17, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {user=******, password=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ]
12

注意：查詢的時候不要使用模糊查詢否則加索引和沒加索引，同樣的效果
3：用多個小表代替一個大表，注意不要過分設計
4：批量插入代替循環單條插入

文章來源於黑馬程序員廣州中心，公總號爲（itheimagz）,已得到轉載受權轉載