How to limit the SQL query result set to Top-N rows only
#SQL:
#PostgreSQL 8.3 and #MySQL:
#Oracle 11g and older versions:
@javaCode☕️
#SQL:
SELECT
title
FROM
post
ORDER BY
id DESC
FETCH FIRST 5 ROWS ONLY#PostgreSQL 8.3 and #MySQL:
SELECT
title
FROM
post
ORDER BY
id DESC
LIMIT 5#Oracle 11g and older versions:
SELECT *
FROM (
SELECT
title
FROM
post
ORDER BY
id DESC
)
WHERE ROWNUM <= 5@javaCode☕️
👍10🤯3👌1
Introduction to PostgreSQL
#PostgreSQL LAG() function provides access to a row that comes before the current row at a specified physical offset. In other words, from the current row the LAG() function can access data of the previous row, or the row before the previous row, and so on.
The LAG() function will be very useful for comparing the values of the current and the previous row.
more info…
@javaCode☕️
LAG() function:#PostgreSQL LAG() function provides access to a row that comes before the current row at a specified physical offset. In other words, from the current row the LAG() function can access data of the previous row, or the row before the previous row, and so on.
The LAG() function will be very useful for comparing the values of the current and the previous row.
more info…
@javaCode☕️
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# What is the difference between JVM Heap and Stack Memory? 🧠
Understanding Memory Allocation in Java ☕
The JVM splits memory into two primary regions: Heap and Stack, each serving distinct purposes in application execution. The #Heap is a shared, runtime memory area where all objects and class instances reside. It's allocated at JVM startup and managed by the #GarbageCollector, which handles automatic deallocation of objects that are no longer referenced. The Heap is further divided into generations (Young, Old, Metaspace in modern JVMs), optimizing garbage collection performance.
The #Stack, in contrast, is thread-private and stores method frames, local variables, and primitive values. Each thread gets its own stack, and memory here follows LIFO (Last In, First Out) methodology. Stack memory is faster but limited in size, throwing #StackOverflowError when exhausted. Unlike Heap objects, stack variables cannot be shared between threads, ensuring thread safety for primitive data.
Key Differences at a Glance 🛠️
- Storage Type: #Heap stores objects and arrays; #Stack stores primitives and object references
- Lifetime: Heap objects live until GC collects them; Stack frames exist only during method execution
- Thread Safety: Heap is shared (requires synchronization); Stack is thread-private by design
- Size: Heap is large (configured via -Xmx); Stack is smaller (configured via -Xss)
- Access Speed: Stack is faster (no GC overhead); Heap is slower (managed by GC)
- Error Types: #OutOfMemoryError (Heap); #StackOverflowError (Stack)
When to Use Which? 🏗️
- Use Heap for: Shared data, large objects, database connections, caching
- Use Stack for: Method-local variables, recursion depth control, thread-safe operations
🔗 Reference: JVM Memory Management Documentation
---
📌 Follow for more Java deep dives!
@javaCode☕
#JVM #Java #MemoryManagement #Heap #Stack #GarbageCollection #Programming #SoftwareEngineering #JavaDeveloper #TechKnowledge
Understanding Memory Allocation in Java ☕
The JVM splits memory into two primary regions: Heap and Stack, each serving distinct purposes in application execution. The #Heap is a shared, runtime memory area where all objects and class instances reside. It's allocated at JVM startup and managed by the #GarbageCollector, which handles automatic deallocation of objects that are no longer referenced. The Heap is further divided into generations (Young, Old, Metaspace in modern JVMs), optimizing garbage collection performance.
The #Stack, in contrast, is thread-private and stores method frames, local variables, and primitive values. Each thread gets its own stack, and memory here follows LIFO (Last In, First Out) methodology. Stack memory is faster but limited in size, throwing #StackOverflowError when exhausted. Unlike Heap objects, stack variables cannot be shared between threads, ensuring thread safety for primitive data.
Key Differences at a Glance 🛠️
- Storage Type: #Heap stores objects and arrays; #Stack stores primitives and object references
- Lifetime: Heap objects live until GC collects them; Stack frames exist only during method execution
- Thread Safety: Heap is shared (requires synchronization); Stack is thread-private by design
- Size: Heap is large (configured via -Xmx); Stack is smaller (configured via -Xss)
- Access Speed: Stack is faster (no GC overhead); Heap is slower (managed by GC)
- Error Types: #OutOfMemoryError (Heap); #StackOverflowError (Stack)
When to Use Which? 🏗️
- Use Heap for: Shared data, large objects, database connections, caching
- Use Stack for: Method-local variables, recursion depth control, thread-safe operations
🔗 Reference: JVM Memory Management Documentation
---
📌 Follow for more Java deep dives!
@javaCode☕
#JVM #Java #MemoryManagement #Heap #Stack #GarbageCollection #Programming #SoftwareEngineering #JavaDeveloper #TechKnowledge