mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
79 lines
1.6 KiB
C
79 lines
1.6 KiB
C
/*-
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* Copyright (c) 1997, 2019 Oracle and/or its affiliates. All rights reserved.
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*
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* See the file EXAMPLES-LICENSE for license information.
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*
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*/
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#include "ex_sql_utils.h"
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/*
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* This example demonstrates the use of indexes.
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* Step 1. Explain a query and output the query plan
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* Step 2. Create an index
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* Step 3. Explain above query again to see how query plan is simplified
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* Step 4. Drop the index
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*/
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/* Example body. */
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static int
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ex_sql_index(db)
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db_handle *db;
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{
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const char* sql_1;
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const char* sql_2;
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/*
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* Explain a query expression to get the query plan.
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*/
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echo_info("STEP1. Explain a query expression");
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sql_1 = "\tEXPLAIN \n"
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"\tSELECT rank, country, name \n"
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"\tfrom university \n"
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"\tWHERE region = 'Europe' \n"
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"\tORDER BY country;";
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exec_sql(db, sql_1);
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/*
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* Now create index.
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*/
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echo_info("STEP2. Create an index on university(region, country)");
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sql_2 = "\tCREATE INDEX university_geo \n"
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"\tON university (region, country);";
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exec_sql(db, sql_2);
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/*
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* Now we check query plan again. We can see reasonable indexes
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* can simplify query plan.
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*/
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echo_info("STEP3. Explain the query again, we can see the difference");
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exec_sql(db, sql_1);
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/*
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* Drop the index.
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*/
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echo_info("STEP4. Drop the index");
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sql_2 = "DROP INDEX university_geo;";
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exec_sql(db, sql_2);
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return 0;
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}
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int
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main()
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{
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db_handle *db;
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/* Setup environment and preload data. */
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db = setup("./ex_sql_index.db");
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load_table_from_file(db, university_sample_data, 1/* Silent */);
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/* Run example. */
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ex_sql_index(db);
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/* End. */
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cleanup(db);
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return 0;
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}
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