In this video, learn about the hash join algorithm.
- [Instructor] Another algorithm … for performing joins is the hash join. … Hash joins use a function to map data … into a value that can act as an index into an array. … Hash functions are designed so that the output value … is virtually unique across all of the values in the domain, … where that is the set of possible input values. … Even slight changes to the input value … can lead to different outputs. … Part of the process of hash joining … is building a table of hash values. … The smaller of the two tables is used. … For each key value in the smaller table, … we compute a hash value and store that in the table. … The next step is called the probe phase. … In this step, we calculate the hash value … of each row, and then look up the corresponding value … in the hash table. … The hash table contains a pointer, … or reference to the location of the row we are joining to. … It's important to note that hash joints … only work with equality conditions. … They don't help when you're using …
Author
Released
4/1/2019- How SQL executes queries
- Working with PostgreSQL tools for tuning
- Bitmap and hash indexes
- Using different types of indexes to improve performance
- Challenges with joining tables
- When to use partitioning to improve performance
- Collecting statistics about data in tables
Skill Level Advanced
Duration
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Introduction
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1. How SQL Executes a Query
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Scanning tables and indexes3m 12s
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Joining tables2m 24s
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Partitioning data2m 23s
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2. PostgreSQL Tools for Tuning
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Installing PostgreSQL2m 41s
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Overview of pgAdmin3m 21s
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Explain and analyze3m 37s
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Indexes3m 7s
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3. Types of Indexes
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Indexing3m 1s
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B-tree indexes2m 2s
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B-tree index example plan2m 18s
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Bitmap indexes1m 46s
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Bitmap index example plan2m 39s
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Hash indexes1m 19s
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Hash index example plan1m 32s
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PostgreSQL-specific indexes1m 17s
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4. Tuning Joins
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Nested loops3m 19s
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Nested loop example plan3m 55s
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Hash joins1m 25s
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Hash join example plan1m 57s
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Merge joins2m 17s
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Merge join example3m 16s
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Subqueries vs. joins1m 11s
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5. Partitioning Data
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Partition by range2m 6s
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Partition by list1m 37s
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Partition by list example4m 55s
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Partition by hash2m 12s
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Partition by hash example4m 51s
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6. Materialized Views
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Materialized views1m 41s
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7. Other Optimization Techniques
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Hints to the query optimizer2m 13s
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Parallel query execution2m 3s
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Miscellaneous tips1m 47s
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Conclusion
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Next steps41s
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Video: Hash joins