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- SQL.How can you compare two nullable values safely, and how does IS DISTINCT FROM differ from <>?
- SQL.How are NULL values ordered by ORDER BY, how do defaults differ between databases, and how can you control their placement?
- SQL.How does NULL propagate through arithmetic expressions, and how can COALESCE and NULLIF help handle missing values and division by zero?
- SQL.How does NULL affect join conditions, and why can filtering the right-hand table in WHERE remove unmatched rows from a LEFT JOIN?
- SQL.How do GROUP BY and DISTINCT treat NULL values, even though NULL = NULL evaluates to UNKNOWN?
- SQL.How do aggregate functions handle NULL, and what is the difference between COUNT(*), COUNT(column), and COUNT(DISTINCT column)?
- SQL.How does NULL affect IN and NOT IN, and why can NOT EXISTS be a safer choice when a subquery returns nullable values?
- SQL.How do WHERE, HAVING, and CHECK constraints treat conditions that evaluate to UNKNOWN?
- SQL.Why do column = NULL and column <> NULL not work as expected, and when should you use IS NULL and IS NOT NULL?
- SQL.What is SQL’s three-valued logic (TRUE, FALSE, UNKNOWN), and how do AND, OR, and NOT behave with UNKNOWN?
- ChromeDevTools.Watch all failed requests
- SQL.What are domain types (or constraints on data types), and how do they help enforce data correctness?
- SQL.How does SQL handle comparisons between different data types (for example, string vs number), and why is this dangerous?
- SQL.What is the difference between DATE, TIME, TIMESTAMP, and TIMESTAMPTZ, and which one should be used for business events?
- SQL.How do numeric types like INTEGER, BIGINT, DECIMAL, and FLOAT differ in terms of precision and use cases?
- SQL.What problems can arise from implicit type casting in SQL, and how can it affect indexes?
- SQL.How does NULL differ from 0, an empty string, or FALSE in SQL?
- SQL.What is the difference between CHAR, VARCHAR, and TEXT, and when would you choose each?
- SQL.What is MVCC ?
- SQL.What is AutoVacuum Postgres ?
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Author Archives: Stanislav_Panteleev
Java.Servlet.How to disable the ability to use EL in JSP?
You can disable EL evaluation in a JSP page by setting the isELIgnored attribute to true in the page directive. ✅ Syntax: This tells the JSP engine to treat ${…} as plain text, not as an EL expression. EL will … Continue reading
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Java.Servlet.Name the implicit, internal JSP EL objects and how they differ from JSP objects.
When you use EL (${…}) in JSP, there are special implicit objects available automatically inside the EL context. ✅ These are different from the classic JSP implicit objects (request, response, session, etc.) you use in Java code inside JSP. 🔵 … Continue reading
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Java.Servlet.What types of EL operators do you know?
In EL (${ … }), you can use many types of operators — very similar to Java, but slightly simplified. Here’s the full organized list: 🔵 1. Arithmetic Operators Operator Description Example + Addition ${2 + 3} → 5 – … Continue reading
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Java.Servlet.What do you know about JSP Expression Language (EL)?
JSP Expression Language (EL) is a simple and powerful way to access Java objects in JSP pages without writing Java code (no <% %> needed). It allows you to access request attributes, session attributes, application attributes, JavaBeans properties, collections, and … Continue reading
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Java.Servlet.Is it possible to define a class inside a JSP page?
✅ Yes, it is technically possible to define a Java class inside a JSP page. You can do it inside a JSP declaration tag: <%! … %>. This code will be inserted into the servlet class that the JSP engine … Continue reading
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Java.Servlet.Why is it not recommended to use scriptlets (script elements) in JSP?
1. 🧹 Mixing Java Code with HTML = Messy and Hard to Maintain When you write Java code directly inside JSP (inside <% … %> blocks),you mix two completely different concerns: Presentation (HTML) Business logic (Java code) Result: Pages become … Continue reading
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Java.Serlet.How to configure initialization parameters for JSP?
Initialization parameters are name–value pairs that are passed to the JSP/servlet when the server loads it. There are two ways to configure them: 🔵 1. Using web.xml (Traditional way) You can define JSP initialization parameters inside the web.xml file of … Continue reading
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Java.Servlet.What do you know about PageContext and what are the advantages of using it?
PageContext is an implicit object available in JSP that acts like a central manager for everything on a JSP page. Think of it as a super helper object that provides: Access to all the other scopes (page, request, session, application) … Continue reading
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Java.Servlet.What implicit objects are not available in a regular JSP page?
👉 The exception object is NOT available in a regular JSP page. Object Available in regular JSP? Notes request ✅ Yes Always response ✅ Yes Always session ✅ Yes Always application ✅ Yes Always out ✅ Yes Always config ✅ … Continue reading
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Java.Servlet.What implicit, internal objects and methods are there in a JSP page?
📜 Implicit Objects in JSP Implicit Objects are automatically created by the JSP container and available to you inside a JSP page without any declaration. You don’t need to create them — they just exist! Here’s the list: Object Type … Continue reading
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