Crashes, No Sound, or Screen Glitches?
Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteWindows Errors? Fix Them Before They Spread
Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallChoose the migration based on what existing rows should contain. If every old row should get the same value, PostgreSQL 11 and later can add a column with a non-volatile constant default without immediately rewriting the table. If the value must be derived separately for each row, add the column as nullable and backfill it in controlled batches before enforcing NOT NULL. PostgreSQL 18 also lets you enforce a NOT NULL constraint before validating existing rows; PostgreSQL 17 does not document that syntax.
Which migration approach fits your data?
Before choosing SQL, answer two questions: what value is correct for rows that already exist, and what should happen to writes made while the migration is underway? A fast schema change is not a substitute for giving historical rows the right meaning.
| Approach | Use it when | Main trade-off |
|---|---|---|
| Non-volatile constant default | Every existing row should have the same value, and the server is PostgreSQL 11 or later. | The add-column operation can avoid an immediate rewrite, but the value must be semantically correct for all old rows. A volatile default follows a per-row path. PostgreSQL: Modifying Tables |
Nullable column, batched backfill, then SET NOT NULL |
Existing rows need distinct or computed values, or a single default would misrepresent them. | The backfill performs real write work; batch size, pacing, retry handling, and monitoring must fit the workload. PostgreSQL does not prescribe a universally safe batch size. PostgreSQL 18: ALTER TABLE |
NOT NULL NOT VALID, then validate |
You run PostgreSQL 18 and need to enforce non-nullness on new writes before checking all existing rows. | Validation still scans existing rows, and the relevant lock behavior must be planned. PostgreSQL 18 Release Notes |
Valid CHECK, then SET NOT NULL |
You need a staged route on PostgreSQL 17, whose documented NOT VALID support covers CHECK and foreign-key constraints, not NOT NULL. |
The check must be validated first. PostgreSQL 17 documents that a valid check proving no null can exist lets SET NOT NULL skip its own table scan. PostgreSQL 17: ALTER TABLE |
Also confirm what concurrent inserts should receive. An application writer, a future default, or an early database constraint may be needed so new or changed rows do not introduce nulls while older rows are being repaired.
When a constant default is the right choice
PostgreSQL 11 introduced a fast path for adding a column with a constant default. For a non-volatile default, PostgreSQL can record the value in metadata for existing rows rather than immediately rewriting every row. When those rows are read, PostgreSQL returns the recorded value; it is materialized physically if the table is rewritten later. This can make the schema change very fast, but it is not a guarantee about total migration time or workload impact. PostgreSQL: Modifying Tables
Recommended Free Tools
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
Use this path only if that one value is actually correct for every historical row. For example, a uniform, valid state assigned to all old records may fit; a value that should reflect each record’s creation time, owner, or other row-specific facts does not.
Volatile defaults change the cost profile. PostgreSQL’s documentation gives clock_timestamp() as an example: it must be calculated for each row, so adding a column with that default requires per-row work rather than the constant-default metadata path. Changing a column’s default later affects future inserts, not the values already represented for old rows. PostgreSQL: Modifying Tables
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
For a uniform value, the conceptual operation is:
ALTER TABLE target_table
ADD COLUMN new_column desired_type DEFAULT 'appropriate_value' NOT NULL;Replace the table, type, and value with your actual schema and data semantics. Check the deployed major-version manual and rehearse the operation on a representative environment.
When historical rows need different values
Do not use an arbitrary placeholder merely to obtain a quick DDL change. Add the column nullable, ensure application writers handle it, backfill existing rows with the correct row-specific expression, and enforce non-nullness once no nulls remain.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
- Add the nullable column:
ALTER TABLE target_table ADD COLUMN new_column desired_type; - Prepare writers: deploy application changes that populate
new_columnon new or changed rows, or establish an appropriate future default if that matches the data model. - Backfill in bounded batches: update subsets of existing rows using the correct row-specific expression. Choose batch size and pacing for the table and workload; the PostgreSQL manual provides no universal safe value.
- Check completion: verify that no rows remain null before applying the final rule.
- Enforce non-nullness: run
ALTER TABLE target_table ALTER COLUMN new_column SET NOT NULL;, or use the PostgreSQL 18 staged constraint route below if early enforcement is required.
This is a schematic outline, not a ready-made batch job. The update predicate, transaction boundaries, retry behavior, and pacing depend on the table and application. Monitor the actual migration, including workload effects and replication lag where relevant.
How to stage enforcement with NOT VALID
NOT VALID separates enforcement for subsequent writes from verification of rows already in the table. PostgreSQL says that adding a NOT VALID constraint skips the initial scan; subsequent inserts and updates are checked, and a later validation checks the pre-existing rows. Validation scans the table and takes a SHARE UPDATE EXCLUSIVE lock. PostgreSQL 18: ALTER TABLE
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
PostgreSQL 18: NOT NULL constraint first
PostgreSQL 18 supports adding a not-null constraint as not valid and validating it later. This lets the database reject nulls from subsequent writes while historical rows are still being checked:
ALTER TABLE target_table
ADD CONSTRAINT target_table_new_column_nn
NOT NULL new_column NOT VALID;
ALTER TABLE target_table
VALIDATE CONSTRAINT target_table_new_column_nn;Use the syntax in the manual for the deployed major version and test it against the actual environment. Adding the constraint does not fill in historical nulls; they must already be absent by validation time.
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
PostgreSQL 17: validated CHECK as the bridge
PostgreSQL 17 documents NOT VALID for check and foreign-key constraints. For a non-null rule, a check constraint can enforce future writes while old rows are brought into compliance, then be validated before setting the column attribute:
ALTER TABLE target_table
ADD CONSTRAINT target_table_new_column_nn_check
CHECK (new_column IS NOT NULL) NOT VALID;
ALTER TABLE target_table
VALIDATE CONSTRAINT target_table_new_column_nn_check;
ALTER TABLE target_table
ALTER COLUMN new_column SET NOT NULL;PostgreSQL 17 documents that a valid check constraint proving no null can exist can allow SET NOT NULL to skip its table scan. This is not the same syntax as PostgreSQL 18’s not-valid not-null constraint. PostgreSQL 17: ALTER TABLE
Plan for scans and locks, not just SQL syntax
Do not describe these migrations as lock-free. PostgreSQL documents lock modes for validation, and most forms of adding a table constraint require an ACCESS EXCLUSIVE lock, with a foreign-key exception. The exact lock requirements depend on the operation and server version. A skipped initial scan can reduce the work performed during constraint installation, but it does not mean the operation takes no lock or that later validation is costless. PostgreSQL 18: ALTER TABLE
Quick Recap
- Confirm the server major version and syntax before deploying, especially if using
NOT VALIDon a not-null constraint. - Rehearse on a representative environment and assess the operation’s lock behavior alongside the backfill workload.
- Set operational timeouts appropriate to your deployment and have a response plan for a migration that waits too long for a lock.
- Monitor progress, application impact, and replication lag during the actual work. Official documentation explains behavior and lock modes but does not establish a duration, row-count threshold, or safe batch size for a particular table.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
