1：当只要一行数据时使用 LIMIT 1
当你查询表的有些时候，你已经知道结果只会有一条结果，但因为你可能需要去fetch游标，或是你也许会去检查返回的记录数。
在这种情况下，加上 LIMIT 1 可以增加性能。这样一样，MySQL数据库引擎会在找到一条数据后停止搜索，而不是继续往后查少下一条符合记录的数据。
[mw_shl_code=applescript,true]SELECT * FROM user WHERE country = 'China'
SELECT 1 FROM user WHERE country = 'China' LIMIT 1[/mw_shl_code]
假如你这边只是为了，查询有没有中国用户存在，那么第二句，效率明显高于第一句。
2：给平凡查询的字段加索引，为了测试先来创建一张表往里面添加100000条记录
CREATE TABLE users(
name VARCHAR(10),
id INT
);插入数据的代码
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();//提交批处理
con.commit();//执行
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();
}
}
}在建索引之前
@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();
}
}运行结果
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运行结果
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：查询的时候不要使用模糊查询不然加索引和没加索引，一样的效果
3：用多个小表代替一个大表，注意不要过度设计
4：批量插入代替循环单条插入
文章来源于黑马程序员广州中心，公总号为（itheimagz）,已获得转载授权转载
