December 08, 2005 06:02PM Re: nested query in mysql 4.0.25-standard Jay Pipes December 08, 2005 08:09PM Re: nested query in mysql 4.0.25-standard Greg Scharlemann December 08, 2005 09:07PM Sorry, you can't reply to this topic. It has been closed....
{ for each row in t3 { for each t1, t2 combination in join buffer { if row satisfies join conditions, send to client } } empty join buffer } } } if buffer is not empty { for each row in t3 { for each t1, t2 combination in join buffer { if row satisfies join conditions, send...
(); System.out.println("Error Code: " + e.getErrorCode()); System.out.println("SQL State: " + e.getSQLState()); // 根据错误信息进行相应的处理 if ("HY000".equals(e.getSQLState())) { // 处理 #HY000 错误 System.out.println("A general or unspecified error occurred in the JDBC...
当然了,MySQL自己在这个算法基础上,演进出了Block Nested-Loop join算法,其实基本上和上面的算法没有区别,伪代码如下: for each row in t1 matching range { for each row in t2 matching reference key { store used columns from t1, t2 in join buffer if buffer is full { for each row in t3 { for...
if buffer is not empty { for each row in t3 { for each t1, t2 combination in join buffer { if row satisfies join conditions, send to client } } } 这个算法,将外层循环的数据缓存在join buffer中,内层循环中的表回合buffer中的数据进行对比,从而减少循环次数,这样便可以提高效率。官网上有个example...
LOGGER.error("MySQL driver not found"); } catch (IOException e) { LOGGER.error("Error reading file " + DB_PROP_PATH); } } public static DatabaseDictionary getInstance() { if (instance == null) { synchronized (DatabaseDictionary.class) { ...
当然了,MySQL自己在这个算法基础上,演进出了Block Nested-Loop join算法,其实基本上和上面的算法没有区别,伪代码如下: foreach rowint1 matching range {foreach rowint2 matching reference key { store used columnsfromt1, t2injoin bufferifbufferisfull {foreach rowint3 {foreach t1, t2 combinationinjoin...
for each row in t1 matching range { for each row in t2 matching reference key { for each row in t3 { if row satisfies join conditions, send to client } } } NLJ アルゴリズムでは、外側のループから内側のループに、一度に 1 つずつ行を渡すため、一般に内側のループで処理されるテ...
* This is typically useful if the policy wants to track usage statistics * in order to make decisions. */ void onUse(Query query); /** Whether the given {@link Query} is worth caching. * This method will be called by the {@link QueryCache} to know whether to ...
ifbuffer isnotempty { foreach rowint3 { foreach t1,t2 combinationinjoin buffer { ifrow satisfies join conditions, send to client } } } 如果t1, t2参与join的列长度只和为s, c为二者组合数, 那么t3表被扫描的次数为 (S*C)/join_buffer_size+1 ...